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   150878篇
  免费   13405篇
  国内免费   9955篇
耳鼻咽喉   1168篇
儿科学   1844篇
妇产科学   2585篇
基础医学   17459篇
口腔科学   2610篇
临床医学   19722篇
内科学   23816篇
皮肤病学   1743篇
神经病学   8005篇
特种医学   5144篇
外国民族医学   82篇
外科学   15375篇
综合类   23903篇
现状与发展   31篇
一般理论   7篇
预防医学   9865篇
眼科学   4166篇
药学   15514篇
  150篇
中国医学   8266篇
肿瘤学   12783篇
  2024年   505篇
  2023年   2371篇
  2022年   5954篇
  2021年   7430篇
  2020年   5522篇
  2019年   4951篇
  2018年   5087篇
  2017年   4650篇
  2016年   4264篇
  2015年   6382篇
  2014年   7976篇
  2013年   7376篇
  2012年   10752篇
  2011年   11694篇
  2010年   7254篇
  2009年   5793篇
  2008年   7619篇
  2007年   7706篇
  2006年   7604篇
  2005年   7432篇
  2004年   5306篇
  2003年   5232篇
  2002年   4479篇
  2001年   3993篇
  2000年   3802篇
  1999年   3879篇
  1998年   2514篇
  1997年   2462篇
  1996年   1780篇
  1995年   1647篇
  1994年   1419篇
  1993年   904篇
  1992年   1378篇
  1991年   1193篇
  1990年   1004篇
  1989年   897篇
  1988年   773篇
  1987年   734篇
  1986年   550篇
  1985年   495篇
  1984年   278篇
  1983年   191篇
  1982年   128篇
  1981年   122篇
  1980年   79篇
  1979年   130篇
  1978年   59篇
  1976年   52篇
  1975年   55篇
  1974年   65篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
BACKGROUND: Rapid, sensitive, specific, and cost-effective screening of donated blood to prevent transmission of infectious agents remains challenging. In recent years, incorporation of nucleic acid testing for HIV-1 and HCV RNA improved blood safety by reducing the window period between infection and serologic detection. For HBV infection, this window period with most serologic assays is 50-60 days. Adding a nucleic acid test (NAT) for HBV DNA with existing NATs for HIV-1 and HCV RNA would further improve blood safety and blood screening efficiency. OBJECTIVE: To evaluate the Procleix Ultrio Assay for simultaneous detection of HIV-1 and HCV RNA and HBV DNA and corresponding discriminatory assays. STUDY DESIGN: The performance of these assays, which utilize the same technology and assay format as the Procleix HIV-1/HCV assay, was determined using relevant clinical specimens and analytical sensitivity and specificity panels. RESULTS: The Procleix Ultrio Assay demonstrated specificity of > or =99.5% in healthy donor blood specimens and in plasma containing potentially interfering substances or other blood-borne pathogens. Assay sensitivity demonstrated >95% detection of 100copies/mL, 30IU/mL, and 15IU/mL for HIV-1 and HCV RNA, and HBV DNA, respectively. The assay detects all known HIV-1 subtypes and HCV and HBV genotypes and is highly reproducible. Statistical analysis using receiver operating characteristic plots demonstrated wide analyte cutoff values for each assay associated with assay specificity and sensitivity of > or =99.5%. CONCLUSIONS: In this investigational study, the Procleix Ultrio Assay sensitivity and specificity were similar to existing NATs used in blood-bank settings to detect HIV-1 and HCV RNA and provided equivalent sensitivity and specificity for detection of HBV DNA. Using this combination assay, blood safety may be improved and the multiplex format enhances blood screening efficiency. The throughput capability of this assay is compatible with large volume processing and the chemistry is adaptable to full automation.  相似文献   
972.
髋关节置换手术中采用标准型假体时,术前只能大致选取假体,术中还要预备多个假体,往往手术时间增长。为了解决这一问题,本文提出一种利用计算机优选标准型髋关节假体的方法。从X线片中获取患者股骨解剖数据。利用这些解剖数据和股骨近端截面平均数据库三维重建患者股骨近端,重建出的股骨近端模型使优选标准假体成为可能。理论分析表明,该方法切实可行。  相似文献   
973.
Yin  Xuewei  Liu  Bin  Wei  Huixia  Wu  Shanshan  Guo  Lijie  Xu  Furu  Liu  TingTing  Bi  Hongsheng  Guo  Dadong 《Inflammation research》2019,68(9):761-774
Objective and design

The present study aimed to investigate the relationship between the disturbed balance of CD4+/CD8+, Th17/Treg and the activation of the Notch signaling pathway in experimental autoimmune uveitis (EAU).

Methods

An EAU rat model was induced in Lewis rats, and pathology analysis was performed by hematoxylin and eosin (H&E) staining. CD4+, CD8+, Th17, and Treg levels in spleen, lymph nodes and eye tissues were determined by flow cytometry. Meanwhile, the expression of Notch1, DLL4, IL-10, and IL-17 was determined by quantitative polymerase chain reaction (Q-PCR) and enzyme-linked immunosorbent assay (ELISA). In addition, the inhibitory effect of N-(N-(3,5-difluorophenacetyl-l-alanyl))-S-phenylglycine t-butyl ester (DAPT) on Th17 differentiation by Notch signaling in vitro was further investigated using T lymphocytes from EAU rats on day 12 post-immunization by flow cytometry.

Results

The pathological results showed that inflammatory cell infiltration occurred in ocular tissues in EAU rats. The CD4+/CD8+ and Th17/Treg ratios in EAU rats were apparently higher than those in normal control individuals. Q-PCR and ELISA analyses indicated the expression of Notch1, DLL4, IL-10, and IL-17 in EAU rats gradually increased on day 6 after immunization, peaked on day 12, and then gradually decreased. The dynamic trends in Notch1 and DLL4 expression in EAU rats were identical to those of CD4+/CD8+ and Th17/Treg levels. DAPT can significantly inhibit the activation of Notch signaling, decrease Th17 cell differentiation, and attenuate the level of the Th17 cell lineage, contributing to the balance of the Th17/Treg ratio.

Conclusion

The activation of the Notch signaling pathway can regulate Th17 and Treg cell differentiation, disrupt the CD4+/CD8+ and Th17/Treg balance, and aggravate the severity of EAU; inactivation of the Notch signaling pathway contributes to the CD4+/CD8+ and Th17/Treg balance in EAU rats. Our findings highlighted that the dynamic change in the CD4+/CD8+ and Th17/Treg ratio was consistent with the expression trend of Notch signaling in EAU rats, suggesting that Notch signaling may be a potentially important therapeutic target in clinical practice.

  相似文献   
974.
凋亡肿瘤细胞负载的树突状细胞对抗原特异性CTL的激活   总被引:4,自引:0,他引:4  
为探讨凋亡Daudi细胞负载的树突状细胞 (DC )激发诱导肿瘤抗原特异性CTL及其生物学特性 ,采用常规方法从人外周血单个核细胞 (PBMC )诱导DC ,激发型CD40mAb联合 50Gyγ射线辐照诱导Daudi凋亡后负载DC ,然后与自体T细胞共育 ,并联合IL 2激发诱导肿瘤特异性CTL ;采用免疫荧光标记和流式细胞仪测定分析膜分子的表达 ;ELISA检测细胞因子的产生 ;Dextran FITC内吞实验分析DC的抗原摄取能力 ;3H掺入试验和51 Cr释放试验分别测定CTL的增殖和细胞毒效应。结果 :(1 )细胞因子序贯体外诱导 7d的DC ,对Dextran吞噬能力最强 ;(2 )CD40mAb诱导联合γ射线辐照 ,能有效介导Daudi细胞的凋亡 ;(3 )抗原负载联合CD40mAb激发可使DC上调表达CD1a、CD80、CD86和HLA DR ,并能促进IL 1 2的分泌 ;(4)凋亡Daudi负载后的DC在激发型CD40mAb作用下 ,能激发和扩增对Daudi细胞具有高效和特异杀伤作用的细胞毒性T细胞。因而认为凋亡肿瘤细胞负载联合CD40mAb刺激的DC可有效激活和扩增肿瘤特异性CTL。  相似文献   
975.
OBJECTIVE: To investigate the relationship between the plasminogen activator inhibitor (PAI-1) polymorphisms and endometrial hypoplasia in infertile women. METHODS: The study was conducted in 105 primary infertile patients with endometrial hypoplasia diagnosed by pathology and the thickness of endometrium by B-mode ultrasound and 85 controls who were not pregnant and had normal fertility. The -675 4G/5G polymorphism in the PAI-1 gene was detected by polymerase chain reaction-restriction fragment length polymerphim analysis. RESULTS: The frequencies of 4G/4G genotype and 4G allele of the PAI-1 gene were higher in the patient group (48.6% and 66.2%) than in the normal controls (22.4% and 47.1%) (P < 0.01). ThePAI-1 4G/4G genotype was significantly associated with endometrial hypoplasia in the infertile patients (OR=4.9, 95% CI: 2.10-10.12). CONCLUSION: The present findings suggest that the 4G/5G polymorphism of the PAI-1 gene was associated with endometrial hypoplasia in infertile patients.  相似文献   
976.
Wu P  Zeng YZ  Wang CM 《Biomaterials》2004,25(6):1123-1130
Lattice constants (LCs) of all possible 96 apatite compounds, A(5)(BO(4))(3)C, constituted by A[double bond]Ba(2+), Ca(2+), Cd(2+), Pb(2+), Sr(2+), Mn(2+); B[double bond]As(5+), Cr(5+), P(5+), V(5+); and C[double bond]F(1-), Cl(1-), Br(1-), OH(1-), are predicted from their elemental ionic radii, using pattern recognition (PR) and artificial neural networks (ANN) techniques. In particular, by a PR study it is demonstrated that ionic radii predominantly govern the LCs of apatites. Furthermore, by using ANN techniques, prediction models of LCs a and c are developed, which reproduce well the measured LCs (R(2)=0.98). All the literature reported on 30 pure and 22 mixed apatite compounds are collected and used in the present work. LCs of all possible 66 new apatites (assuming they exist) are estimated by the developed ANN models. These proposed new apatites may be of interest to biomedical research especially in the design of new apatite biomaterials for bone remodeling. Similarly these techniques may also be applied in the study of interface growth behaviors involving other biomaterials.  相似文献   
977.
BACKGROUND AND PURPOSE: Systemic lupus erythematosus (SLE), a prototype of systemic autoimmune disease characterized by multiorgan involvement with diverse clinical and serological manifestations, principally affects women in their child-bearing years. Clinically significant hepatic abnormality as the initial presentation of SLE has rarely been reported. METHODS: Eleven patients with lupus with initial presentation of lupus-related hepatitis were included in this retrospective review. Clinical manifestation, immunological profiles, and risk factors for poor prognosis were analyzed. RESULTS: The most commonly associated clinical manifestations were found to be thrombocytopenia, leukopenia, advancing age, and presence of anti-SSA/Ro antibody and anti-thyroid antibodies. The diagnosis of SLE was delayed due to dominant hepatic abnormalities. Age greater than 50 years and marked hepatic decompensation in accordance with Child classification B and C might suggest poor prognosis (p=0.06). However, the p value was not statistically significant because of the small sample size. CONCLUSIONS: Lupus-related hepatitis, particularly in late-onset lupus, is common. In addition, the presence of anti-SSA, anti-thyroglobulin, and anti-microsomal antibodies is indicative of hepatic involvement in patients with SLE.  相似文献   
978.
Spouse-spouse, sib-sib, and parent-offspring correlations were calculated for urinary, plasma, and intracellular sodium levels on over 1,900 persons aged 3-86 years in 98 Utah kindreds. For 36 hours prior to their clinic visit, 31% of the sample was salt-loaded with salt tablets, while the rest followed their normal diet. For those on their normal diet, urine creatine-, age-, and sex-adjusted urinary sodium excretion from a timed 12-hour overnight sample showed similar and significant correlations between spouses (r = .29), sibs less than 20 years old (r = .38), and parent-offspring pairs for offspring less than 20 years old (r = .29). This contrasted with the lower correlations between sibs 20 years of age and older (r = .10) and parent-offspring pairs for offspring 20 years of age and older (r = .13), presumed to live in different households. Adult plasma sodium sib-sib (r = .13) and parent-offspring (r = .15) correlations were similar to the urinary sodium correlations, while the spouse-spouse (r = .48), the sib-sib (r = .64), and the parent-offspring (r = .63) correlations for those presumed to live in the same household nearly doubled. Intracellular sodium correlations for the adult sibs (r = .32) and offspring (r = .36) were over twice as large as for urinary or plasma sodium, although the spouse-spouse correlation (r = .37) remained large also.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
979.
In the present study, we used both histidine decarboxylase-deficient (HDC-KO) mice and wild-type (WT) mice to elucidate the possible role of carnosine in pentylenetetrazol (PTZ)-induced seizures. In the acute PTZ challenge study, PTZ (75 mg/kg) was injected intraperitoneally (i.p.) to induce seizures. Carnosine (200, 500 or 1000 mg/kg, i.p.) significantly decreased seizure stage, and prolonged the latency for myoclonic jerks in WT mice in a dose-dependent manner. The effects of carnosine (500 mg/kg) were time-dependent and reached a peak at 1 h. However, it had no significant effect on HDC-KO mice. Carnosine (500 mg/kg) also significantly elevated the thresholds in WT mice but not HDC-KO mice following intravenous (tail vein) administration of PTZ. We also found that α-fluoromethylhistidine substantially reversed the protective effects of carnosine in WT mice. In addition, carnosine pretreatment reduced the cortical EEG activity induced by PTZ (75 mg/kg, i.p.). These results indicate that carnosine can protect against PTZ-induced seizures and its action is mainly through the carnosine–histidine–histamine metabolic pathway. This suggests that carnosine may be an endogenous anticonvulsant factor in the brain and may be used as a new antiepileptic drug in the future.  相似文献   
980.
We report here the molecular cloning of a newly identified preprotachykinin gene, Pptc, which specifies the sequence for a new preprotachykinin protein and bioactive peptide designated hemokinin 1 (HK-1). PPT-C mRNA was detected primarily in hematopoietic cells in contrast to the previously described Ppta and Pptb genes, which are predominantly expressed in neuronal tissues. HK-1 has several biological activities that are similar to the most studied tachykinin, substance P, such as induction of plasma extravasation and mast cell degranulation. However, HK-1 also has properties that are indicative of a critical role in mouse B cell development. HK-1 stimulated the proliferation of interleukin 7-expanded B cell precursors, whereas substance P had no effect. HK-1, but not substance P, promoted the survival of freshly isolated bone marrow B lineage cells or cultured, lipopolysaccharide-stimulated pre-B cells. N-acetyl-L-trytophan-3,5-bistrifluromethyl benzyl ester, a tachykinin receptor antagonist, increased apoptosis of these cells and in vivo administration of this antagonist led to specific reductions of the B220lowCD43 population (the pre-B cell compartment) in the bone marrow and the IgMhighIgDlow population (the newly generated B cells) in the spleen. Thus, HK-1 may be an autocrine factor that is important for the survival of B cell precursors at a critical phase of development.  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