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   6508篇
  免费   717篇
  国内免费   21篇
耳鼻咽喉   48篇
儿科学   195篇
妇产科学   120篇
基础医学   1147篇
口腔科学   145篇
临床医学   660篇
内科学   1161篇
皮肤病学   74篇
神经病学   676篇
特种医学   425篇
外科学   643篇
综合类   182篇
一般理论   5篇
预防医学   579篇
眼科学   196篇
药学   591篇
中国医学   1篇
肿瘤学   398篇
  2021年   83篇
  2019年   73篇
  2018年   83篇
  2017年   73篇
  2016年   69篇
  2015年   84篇
  2014年   108篇
  2013年   223篇
  2012年   253篇
  2011年   238篇
  2010年   157篇
  2009年   156篇
  2008年   236篇
  2007年   254篇
  2006年   261篇
  2005年   327篇
  2004年   288篇
  2003年   272篇
  2002年   243篇
  2001年   210篇
  2000年   237篇
  1999年   214篇
  1998年   102篇
  1997年   107篇
  1996年   130篇
  1995年   91篇
  1994年   87篇
  1993年   91篇
  1992年   172篇
  1991年   142篇
  1990年   134篇
  1989年   139篇
  1988年   135篇
  1987年   135篇
  1986年   124篇
  1985年   127篇
  1984年   101篇
  1983年   98篇
  1982年   56篇
  1980年   66篇
  1979年   93篇
  1978年   59篇
  1977年   60篇
  1976年   57篇
  1975年   53篇
  1974年   56篇
  1973年   65篇
  1971年   54篇
  1969年   53篇
  1968年   55篇
排序方式: 共有7246条查询结果,搜索用时 15 毫秒
31.
HLA-A, -B, -C, -DR, and -DQ typings of the Schmiedeleut Hutterites of South Dakota were collected as part of an ongoing genetic-epidemiologic study of HLA and fertility. A total of 1,082 individuals, including 852 married adults representative of the reproductive population of this isolate, were characterized for five-locus HLA haplotypes. HLA-A1, A2, A3, and A24 accounted for 75% of observed HLA-A alleles and HLA-B27, B35, B51, and B62 accounted for 55% of observed HLA-B alleles. S-leut Hutterites are derived from 68 or fewer ancestors. However, only 48 ancestral HLA haplotypes were observed and nine of these accounted for over 52% of the observed haplotypes. Measures of two-locus linkage disequilibrium derived from these haplotypes indicated that one-third to half of the observed HLA-A/B, B/DR, and A/DR allele combinations exhibited highly statistically significant linkage disequilibrium. Allele and haplotype frequencies did not differ between males and females. Recombination rates of 0.004% and 0.005% between HLA-A and -C and between HLA-B and -DR, respectively, were observed. This HLA profile points out a paucity of HLA alleles and haplotypes in this population and marked linkage disequilibrium among the HLA alleles that are present. © Wiley-Liss, Inc.  相似文献   
32.
Image quality and safety of magnetic resonance (MR) imaging were evaluated in vitro and in eight patients with the most commonly employed metallic biliary endoprosthesis. In vitro, the stent produced no tip deflection at 0.6 or 1.5 T. Trace magnetic susceptibility artifact, similar to artifact from a column of air, paralleled the stent. In patients, image degradation was minimal with conventional pulse sequences. Middle-field-strength spin-echo images revealed minimal artifacts indistinguishable from those produced by pneumobilia.  相似文献   
33.
34.
The beta-adrenergic receptor kinase (beta ARK) phosphorylates the agonist-occupied beta-adrenergic receptor to promote rapid receptor uncoupling from Gs, thereby attenuating adenylyl cyclase activity. Beta ARK-mediated receptor desensitization may reflect a general molecular mechanism operative on many G-protein-coupled receptor systems and, particularly, synaptic neurotransmitter receptors. Two distinct cDNAs encoding beta ARK isozymes were isolated from rat brain and sequenced. The regional and cellular distributions of these two gene products, termed beta ARK1 and beta ARK2, were determined in brain by in situ hybridization and by immunohistochemistry at the light and electron microscopic levels. The beta ARK isozymes were found to be expressed primarily in neurons distributed throughout the CNS. Ultrastructurally, beta ARK1 and beta ARK2 immunoreactivities were present both in association with postsynaptic densities and, presynaptically, with axon terminals. The beta ARK isozymes have a regional and subcellular distribution consistent with a general role in the desensitization of synaptic receptors.  相似文献   
35.
Many conventional dressings are painful when removed, and may be detrimental to healing. In a pilot study ten consecutive abscesses, requiring incision and drainage, were packed with a calcium alginate dressing: this was well tolerated, its removal causing minimal pain. No adverse effects were attributable to its use. A controlled trial was therefore carried out to compare calcium alginate with the more traditional saline-soaked gauze for packing abscess cavities, following incision and drainage. Patients were randomized to receive either calcium alginate (16 patients) or gauze dressing (18 patients). At the first dressing change the patient marked on a linear analogue scale the pain experienced; the nurse noted similarly the ease of removal of the dressing. Calcium alginate was significantly less painful to remove after operation (P less than 0.01), and also easier to remove (P less than 0.01) than gauze dressings. If abscess cavities are packed after incision and drainage, calcium alginate appears to be an improvement on conventional dressings.  相似文献   
36.
Normal adult human thyroid follicular cells have an extremely limited proliferative capacity in vitro. No previously studied mitogen, including thyrotropin (TSH) or epidermal growth factor (EGF), has in our hands resulted in a significant improvement over the 3-4% nuclear [3H]thymidine pulse-labelling index (LI) obtainable with 10% fetal calf serum. Here we report the detection in the conditioned medium from a sub-clone of NIH3T3 fibroblasts of a mitogenic activity capable of increasing this response up to 10-fold, to an LI of over 20%, together with an even greater relative stimulation of mitotic activity. Preliminary characterisation has excluded EGF and TGF alpha, and demonstrated that the activity is bound reversibly by heparin-Sepharose, thus pointing to a member of the heparin-binding fibroblast- or hepatocyte-growth factor families. This material should have wide practical application in facilitating primary culture of follicular cells, and may reveal new mechanisms of stromal-epithelial interaction regulating normal and neoplastic thyroid growth in vivo.  相似文献   
37.
A patient with acute peritonitis due to ovarian actinomycosis and the association of this disease with the intrauterine contraceptive device is discussed. Because adequate treatment requires prolonged antibiotics the diagnosis should be sure. Unfortunately if antibiotics are given pre-operatively culture is usually unsuccessful and thus careful examination of all removed material is essential. As many of these women are of child bearing age surgical intervention should aim to preserve fertility wherever possible.  相似文献   
38.
AIM:To determine if novel bile acid transporters may be expressed in human tissues.METHODS:SLC10A1 (NTCP) was used as a probe to search the NCBI database for homology to previously uncharacterized ESTs. The homology search identified an EST (termed SLC10A4) that shares sequence identity with SLC10A1 and SLC10A2 (ASBT). We performed Northern blot analysis and RT-PCR to determine the tissue distribution of SLC10A4. SLC10A4 was cloned in frame with an epitope tag and overexpressed in CHO cells to determine cellular localization and functional analysis of bile acid uptake.RESULTS:Northern analysis revealed that SLC 10A4 mRNA is ubiquitously expressed fn human tissues with the highest levels of mRNA expression in brain,placenta, and liver. In SLC10A4-transfected CHO cells,immunoblotting analysis and immunofluorescence staining demonstrated a 49-kDa protein that is expressed at the plasma membrane and intracellular compartments.Functional analysis of SLC10A4 showed no significant taurocholate uptake in the presence of sodium when compared to untransfected CHO cells.CONCLUSION:To date, we have shown that this protein has no capacity to transport taurocholate relative to SLC1041; however, given its ubiquitous tissue distribution, it may play a more active role in transporting other endogenous organic anions.  相似文献   
39.
40.
Absorption of elemental iron from three single-daily-dose prenatal multivitamin/multimineral supplements was compared in bioavailability studies of subjects under fasting and postprandial conditions. Each of the supplements (Stuartnatal 1 + 1, Stuart Prenatal, and Materna 1.60) contained 60 or 65 mg of iron. The subjects, teenagers in the second trimester of pregnancy, were assigned to the fasting or postprandial conditions at intervals of three to seven days. For the postprandial condition, subjects took the supplement after eating a standardized meal that had been designed to provide a minimal amount of iron and no caffeine (which inhibits iron absorption); blood was drawn at 0, 1, 3, 6, and 8 hours. Bioavailability studies showed that all three supplements provided adequate levels (at least 3.5 mg) of absorbed iron when taken postprandially. The highest quantity of net iron transport as well as the most rapid intestinal transport in either condition was yielded by Stuartnatal 1 + 1 taken in the fasting state. In the postprandial condition, Materna 1.60 demonstrated the fastest transport time and highest net iron transport; when given to a subject in the fasting condition, however, this supplement provided less than the recommended 3.5 mg of absorbed iron. These results suggest that iron absorption is influenced by supplement formulation as well as the presence or absence of food. Considering variations in compliance when iron is to be taken on an empty stomach as well as variable absorption in the fasting state, the most reliable supplementation would appear to be achieved by instructing pregnant women to take multivitamin/multimineral supplements at mealtime.  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