首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5994篇
  免费   385篇
  国内免费   152篇
耳鼻咽喉   129篇
儿科学   104篇
妇产科学   23篇
基础医学   745篇
口腔科学   121篇
临床医学   499篇
内科学   524篇
皮肤病学   261篇
神经病学   845篇
特种医学   81篇
外科学   575篇
综合类   520篇
预防医学   344篇
眼科学   157篇
药学   1151篇
中国医学   364篇
肿瘤学   88篇
  2024年   37篇
  2023年   85篇
  2022年   230篇
  2021年   295篇
  2020年   226篇
  2019年   172篇
  2018年   142篇
  2017年   154篇
  2016年   189篇
  2015年   234篇
  2014年   317篇
  2013年   406篇
  2012年   258篇
  2011年   312篇
  2010年   290篇
  2009年   276篇
  2008年   288篇
  2007年   259篇
  2006年   301篇
  2005年   223篇
  2004年   194篇
  2003年   205篇
  2002年   151篇
  2001年   136篇
  2000年   104篇
  1999年   107篇
  1998年   87篇
  1997年   86篇
  1996年   63篇
  1995年   62篇
  1994年   59篇
  1993年   49篇
  1992年   63篇
  1991年   42篇
  1990年   65篇
  1989年   40篇
  1988年   36篇
  1987年   40篇
  1986年   32篇
  1985年   45篇
  1984年   25篇
  1983年   19篇
  1982年   39篇
  1981年   20篇
  1980年   17篇
  1979年   13篇
  1978年   7篇
  1977年   9篇
  1976年   9篇
  1974年   6篇
排序方式: 共有6531条查询结果,搜索用时 19 毫秒
101.
①目的 建立一种简单、灵敏、高效的测定粮食中雪腐镰刀菌烯醇 (NIV )、脱氧雪腐镰刀菌烯醇(DON)、新茄病镰刀菌烯醇 (NS)的方法。②方法 粮食样品用甲醇 水 (95∶5 ,V∶V)提取 ,经Florisil柱净化 ,用 9∶1的氯仿 甲醇进行洗脱 ,提取液经n 7氟丁酰咪唑衍生后 ,用配有SE 5 4弹性石英毛细管柱的气相色谱进行测定 ,检测器为电子捕获检测器。③结果 建立了粮食中 3种镰刀菌毒素的气相色谱测定方法 ,其最低检测限为 1×10 -11~ 1× 10 -10 g ,各毒素回收率均在 85 %以上。④结论 该方法灵敏、简单、快速、回收率高 ,具有很好的实际应用价值。  相似文献   
102.
BACKGROUND: AbobotulinumtoxinA (AboBoNT-A; Dysport®; Ipsen, Boulogne-Billancourt, France/Azzalure®; Galderma, Lausanne, Switzerland) is a botulinum neurotoxin type A approved for aesthetic use in the treatment of glabellar lines in adult patients under 65 years in Europe, the United States, and other countries. OBJECTIVE: We sought to analyze current literature on patient satisfaction with aboBoNT-A for upper facial aesthetic indications. METHODS: A systematic review of literature databases (PubMed/MEDLINE, Embase, the Cochrane Library, and Google Scholar) was performed to identify English-language publications reporting on patients with aesthetic indications (including glabellar lines and wrinkles) receiving aboBoNT-A, that assessed patient and/or physician satisfaction with treatment, with no restrictions on comparator studies. Structured data extraction was used to enable inter-study analysis. A post-hoc analysis was also performed to assess patient satisfaction by sex and age, using results from the noninterventional APPEAL study of patients’ satisfaction with aboBoNT-A for treating glabellar lines. RESULTS: Overall, 22 original research papers were identified. Patient satisfaction rates for aboBoNT-A treatment were significantly higher versus placebo from two weeks to between three and five months postinjection. At two to three weeks postinjection, patient satisfaction rates were 52% and 99% across studies. In studies with later time points, patient satisfaction rates were 85 to 87 percent at 5 months and between 25 and 100 percent at 6 months post-injection. Physician satisfaction was also high (97%–100%, across three treatments). No notable differences in patient satisfaction by sex or age were observed in the APPEAL study. CONCLUSION: High rates of patient satisfaction have been achieved with aboBoNT-A treatment for upper facial aesthetic indications. Despite the current recommended interval of ≥12 weeks, satisfaction with the aesthetic results of aboBoNT-A therapy is still evident up to 6 months post-injection in some patients.  相似文献   
103.
《Vaccine》2021,39(44):6545-6552
BackgroundExploring factors that affect immune responses to immunizations in infants born to women immunized with tetanus-diphtheria-acellular-pertussis (Tdap) in pregnancy compared with unimmunized women is important in designing immunization programs.MethodsIndividual-participant data meta-analysis of 8 studies reporting post-immunization immunoglobulin G (IgG) levels to vaccine antigens in infants born to either women immunized with Tdap in pregnancy or unimmunized women, using mixed-effects models.ResultsIn infants of Tdap-immunized women, two-fold higher levels of anti-pertussis toxin (PT) and anti-diphtheria-toxoid (DT) IgG pre-primary immunization were associated with 9% and 10% lower post-primary immunization levels, (geometric mean ratio [GMR], PT: 0.91; 95% CI, 0.88–0.95,n = 494, DT: 0.9; 0.87–0.93,n = 519). Timing of immunization in pregnancy did not affect post-primary immunization anti-Bordetella pertussis, anti-tetanus-toxoid (TT) and anti-DT IgG levels. Spacing of infant immunization did not affect post-primary immunization anti-B. pertussis and anti-DT levels. In infants of Tdap-immunized women, two-fold higher levels of anti-PT and anti-filamentous haemagglutinin (FHA) IgG pre-primary immunization were associated with lower post-booster immunization levels, (GMR, PT: 0.91; 0.85–0.97,n = 224, FHA: 0.92; 0.85–0.99,n = 232). Timing of immunization in pregnancy did not affect post-booster immunization anti-Bordetella pertussis, anti-tetanus-toxoid (TT) and anti-DT IgG levels. Spacing of infant immunization did not affect post-booster immunization anti-PT, anti-pertactin (PRN), anti-TT and anti-DT IgG levels.In infants of unimmunized women, two-fold higher IgG levels of some vaccine antigens pre-primary immunization were associated with 8–17% lower post-primary immunization levels (GMR, PT 0.92, 95% CI:0.88–0.97, n = 373; FHA:0.88, 95% CI:0.85–0.92,n = 378; PRN:0.84, 95% CI:0.81–0.88, n = 367; TT:0.88, 95% CI:0.83–0.93, n = 241; DT: 0.83, 95% CI:0.79–0.87,n = 278). Two-fold higher levels of anti-FHA IgG pre-primary immunization were associated with 8% lower post-booster immunization levels (GMR, 0.92; 95% CI: 0.86–0.99,n = 138).DiscussionIncreased IgG levels pre-primary immunization is associated with reduced post-primary and post-booster immunization levels for some antigens in infants of women immunized or unimmunized in pregnancy, but their clinical significance is uncertain.  相似文献   
104.
Activation of KCNQ potassium channels by stimulation of co-expressed dopamine D2 receptors was studied electrophysiologically in Xenopus laevis oocytes and in mammalian cells. To address the specificity of the interaction between D2-like receptors and KCNQ channels, combinations of KCNQ1–5 channels and D2-like receptors (D2L, D3, and D4) were investigated in Xenopus oocytes. Activation of either receptor with the selective D2-like receptor agonist quinpirole (100 nM) stimulated all the KCNQ currents, independently of the subunit combination, indicating a common pathway of receptor-channel interaction. The KCNQ4 current was investigated in further detail and was increased by 19.9±1.6% (n=20) by D2L receptor stimulation. The effect could be mimicked by injection of GTPS and prevented by injection of Bordetella pertussis toxin, indicating that channel stimulation was mediated via a G protein of the Gi/o subtype. Cells of the human neuroblastoma line SH-SY5Y were co-transfected transiently with KCNQ4 and D2L receptors. Stimulation of D2L receptors increased the KCNQ4 current (n=6) as determined in whole-cell patch-clamp recordings. The specificity of the dopaminergic activation of the KCNQ channels was confirmed by co-expression of other neuronal K+ channels (BK, KV1.1, and KV4.3) with the D2L receptor in Xenopus oocytes. None of these K+ channels responded to stimulation of the D2L receptor. In the mammalian brain, dopamine D2 receptors and KCNQ channels co-localise postsynaptically in several brain regions, so modulation of neuronal excitability by dopamine release could in part be mediated via an effect on KCNQ channels.  相似文献   
105.
The organization of the thalamic projections to the ventral striatum in the rat was studied by placing injections of the retrograde tracer cholera toxin subunit B in the ventral striatum and small deposits of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHA-L) in individual midline and intralaminar thalamic nuclei. In order to provide a complete map of the midline and intralaminar thalamostriatal projections, PHA-L injections were also made in those parts of the intralaminar nuclei that project to the dorsal striatum. The relationship of thalamic afferent fibres with the compartmental organization of the ventral striatum was assessed by combining PHA-L tracing and enkephalin immunohistochemistry. The various midline and intralaminar thalamic nuclei project to longitudinally oriented striatal sectors. The paraventricular thalamic nucleus sends most of its fibres to medial parts of the nucleus accumbens and the olfactory tubercle, whereas smaller contingents of fibres terminate in the lateral part of the nucleus accumbens and the most ventral, medial, and caudal parts of the caudate-putamen complex. The projections of the parataenial nucleus are directed towards central and ventral parts of the nucleus accumbens and intermediate mediolateral parts of the olfactory tubercle. The intermediodorsal nucleus projects to lateral parts of the nucleus accumbens and the olfactory tubercle and to ventral parts of the caudate-putamen. The projection of the rhomboid nucleus is restricted to the rostrolateral extreme of the striatum. A diffuse projection to the ventral striatum arises from neurons ventral and caudal to the nucleus reuniens rather than from cells inside the nucleus. Fibres from the central medial nucleus terminate centrally and dorsolaterally in the rostral part of the nucleus accumbens and medially in the caudate-putamen. Successively more lateral positions in the caudate-putamen are occupied by fibres from the paracentral and central lateral nuclei, respectively. The lateral part of the parafascicular nucleus projects to the most lateral part of the caudate-putamen, whereas projections from the medial part of this nucleus terminate in the medial part of the caudate-putamen and in the dorsolateral part of the nucleus accumbens. Furthermore, a rostral to caudal gradient in a midline or intralaminar nucleus corresponds to a dorsal to ventral and rostral to caudal gradient in the striatum. In the ventral striatum, thalamic afferent fibres in the "shell" region of the nucleus accumbens avoid areas of high cell density and weak enkephalin immunoreactivity.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
106.
Summary We have identified a strain of the yeast Pichia acaciae which produces a killer toxin active against the yeast Debaryomyces tamarii. The killer phenotype was associated with the presence of two DNA plasmids, pPacl-1 (13.6 kilobase pairs) and pPacl-2 (7.3 kilobase pairs). P. acaciae strains, cured of these plasmids by irradiation with ultraviolet light, lacked killer activity and were sensitive to toxin produced by the parental strain. A partially cured strain, GS-1215, missing only the smaller plasmid, pPacl-2, also exhibited loss of both toxin activity and immunity. Exonuclease studies revealed that both plasmids were linear double-stranded DNA molecules with 5 protected ends. The P. acaciae system differs from that of the well-studied Kluyveromyces lactis killer system both in the range of susceptible strains and in the sizes of the plasmids involved. Our studies contradict previous reports that Pichia killer systems are invariably chromosomal.  相似文献   
107.
One of the requirements for an agent to cause hemolytic uremic syndrome (HUS) is its ability to injure endothelial cells. Shiga-like toxin (SLT) can do this. SLT is produced byEscherichia coli andShigella dysenteriae serotype 1; both have been implicated as causes of typical HUS. Endothelial cells have receptors (GB3) for SLT and the toxin can inhibit eukaryotic protein synthesis, thereby causing cell death. Glomerular endothelial cell injury or death results in a decreased glomerular filtration rate and many of the perturbations seen in HUS. It is no longer certain that hemolysis is the result of a microangiopathy. Cell injury results in release of von Willebrand multimers; if these are ultra-large, thrombosis may ensue. There is also increasing evidence that neutrophils have a role in the pathogenesis of typical HUS.Streptococcus pneumoniae can also cause HUS and care must be taken to avoid giving plasma to patients withS. pneumoniae-associated HUS. There is compelling evidence that types of HUS are inherited by autosomal recessive and autosomal dominant modes. Patients with autosomal recessive HUS may have recurrent episodes. Mortality and morbidity rates are high for the inherited forms.  相似文献   
108.
目的 :对细菌内毒素检查法在临床的应用进行探讨。方法 :参照中国药典九五版 (二部 )中的有关细菌内毒素检查法规定 ,采用最大有效稀释倍数法进行干扰实验。结果 :通过对 3 0批大输液进行细菌内毒素检查 ,甘露醇注射液 6批 ,阴性 6批 ;葡萄糖氯化纳注射液 1 8批 ,阴性 1 8批 ;低分子右旋糖酐注射液 6批 ,阳性 1批 ,阴性 5批。结论 :细菌内毒素检查法灵敏、方便、快捷 ,有利于大输液成品的质量控制。  相似文献   
109.
  1. The activation of G proteins by type 1α metabotropic glutamate receptors (mGluRs) in membranes from recombinant baby hamster kidney cells expressing the cloned rat mGluR1α receptor has been studied by use of a [35S]-guanosine 5′-[γ-thio]triphosphate ([35S]-GTPγS) binding assay.
  2. L-Glutamate increased the rate of [35S]-GTPγS binding in a concentration-dependent manner (−logEC50 (M) 5.25±0.07), with an optimal (62.4±1.6%) increase over basal binding being observed following 60 min incubation at 30°C with 70 pM [35S]-GTPγS, 1 μM GDP, 10 mM MgCl2, 100 mM NaCl and 100 μg membrane protein ml−1. The L-glutamate (100 μM)-stimulated increase in [35S]-GTPγS binding was totally prevented in the presence of the group I mGluR antagonist (S)-4-carboxy-3-hydroxyphenylglycine (300 μM).
  3. Quantitative analysis of the affinity and number of G proteins activated by a maximally effective concentration of L-glutamate revealed an equilibrium dissociation constant (KD) for [35S]-GTPγS binding of 0.76±0.20 nM and a maximal number of GTPγS-liganded G proteins (Bmax) of 361±30 fmol mg−1 protein.
  4. Metabotropic glutamate receptor agonists, quisqualate (−logEC50 (M) 6.74±0.06), 1S,3R-ACPD (4.64±0.08) and (S)-3,5-dihydroxyphenylglycine (5.16±0.23) also increased [35S]-GTPγS binding in a concentration-dependent manner, with the latter two agents behaving as partial agonists.
  5. (+)-α-Methylcarboxyphenylglycine (300 μM) caused a parallel rightward shift of the L-glutamate concentration-effect curve for [35S]-GTPγS binding, allowing an antagonist equilibrium dissociation constant (KD) of 34.0±7.8 μM to be calculated for this mGluR antagonist.
  6. Pretreatment of BHK-mGluR1α cells with a concentration of pertussis toxin (PTX) shown to be maximally effective (100 ng ml−1, 24 h) before membrane preparation resulted in a marked decrease in agonist-stimulated [35S]-GTPγS binding (by 66.0±0.9%), and an altered concentration-effect relationship for agonist-stimulated [35S]-GTPγS binding by the residual PTX-insensitive G-protein population.
  7. The modulation of [35S]-GTPγS binding by agonists and antagonists in membranes from recombinant cells provides an excellent system in which to study mGluR interactions with PTX-sensitive and -insensitive G proteins.
  相似文献   
110.
We observed that peripheral T cells activated in vivo or invitro by superantigens are susceptible to cell death when theirantigen receptor is cross-linked with the appropriate anti-ßTCR mAb. TCR ligation by mAbs specifically drove the T cellclonal deletion in both CD4+ and CD8+ cell subsets. An IL-2/1L-2Rinteraction seems to be a critical step In predisposing superantigenactivated cells to death; In fact, in vivo IL-2R bockade reversedT cell deletion In superantlgen plus anti-ß TCR mAbtreated mice. TCR ligatlon by mAbs also produced cell deathof the relevant targets in in vitro IL-2 activated T cells.Surprisingly, no T cell deletion was demonstrable in IL-2 activatedcells following staphylococcal enterotoxin B - TCR Interaction,ruling out the possibility that superantigen in Itself can inducecell death. Thus, while superantigen activation opens the celldeath program, a subsequent TCR-antigen (self) Interaction appearsnecessary to produce clonal deletion in mature T lymphocytes.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号