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   6011篇
  免费   577篇
  国内免费   1篇
  2022年   40篇
  2021年   74篇
  2020年   46篇
  2019年   60篇
  2018年   58篇
  2017年   54篇
  2016年   110篇
  2015年   208篇
  2014年   208篇
  2013年   283篇
  2012年   376篇
  2011年   424篇
  2010年   251篇
  2009年   226篇
  2008年   312篇
  2007年   365篇
  2006年   331篇
  2005年   357篇
  2004年   365篇
  2003年   336篇
  2002年   371篇
  2001年   96篇
  2000年   75篇
  1999年   110篇
  1998年   86篇
  1997年   75篇
  1996年   67篇
  1995年   56篇
  1994年   65篇
  1993年   65篇
  1992年   64篇
  1991年   57篇
  1990年   54篇
  1989年   55篇
  1988年   51篇
  1987年   58篇
  1986年   48篇
  1985年   43篇
  1984年   54篇
  1983年   49篇
  1982年   48篇
  1981年   55篇
  1980年   36篇
  1979年   39篇
  1978年   42篇
  1977年   39篇
  1976年   43篇
  1974年   26篇
  1973年   40篇
  1972年   25篇
排序方式: 共有6589条查询结果,搜索用时 15 毫秒
1.
2.
3.
Dominant males of nonseasonally breeding species should have more opportunity than seasonal breeders to monopolize access to estrous females and thus enhance their reproductive success. They may also use other strategies for maximizing reproductive success such as producing offspring by relatively high ranking females. To test these hypotheses, the paternity of 35 (80%) of 44 Macaca fascicularis offspring, born over a 28-month period, was established using electrophoretically and serologically defined genetic markers. The social ranks of each of the seven potential fathers and 26 potential mothers were determined by recording outcomes of dyadio agonistic interactions. No evidence could be found to support either hypothesis. Further, in view of previously reported significant, positive correlations between male social rank and sexual activity rates in this study group, sexual activity rates do not appear to predict the number of offspring a male sires in this species.  相似文献   
4.
There is an urgent need for effective prophylactic measures against Mycobacterium tuberculosis (Mtb) infection, particularly given the highly variable efficacy of Bacille Calmette-Guerin (BCG), the only licensed vaccine against tuberculosis (TB). Most studies indicate that cell-mediated immune responses involving both CD4+ and CD8+ T cells are necessary for effective immunity against Mtb. Genetic vaccination induces humoral and cellular immune responses, including CD4+ and CD8+ T-cell responses, against a variety of bacterial, viral, parasitic and tumor antigens, and this strategy may therefore hold promise for the development of more effective TB vaccines. Novel formulations and delivery strategies to improve the immunogenicity of DNA-based vaccines have recently been evaluated, and have shown varying degrees of success. In the present study, we evaluated DNA-launched Venezuelan equine encephalitis replicons (Vrep) encoding a novel fusion of the mycobacterial antigens α-crystallin (Acr) and antigen 85B (Ag85B), termed Vrep-Acr/Ag85B, for their immunogenicity and protective efficacy in a murine model of pulmonary TB. Vrep-Acr/Ag85B generated antigen-specific CD4+ and CD8+ T cell responses that persisted for at least 10 wk post-immunization. Interestingly, parenterally administered Vrep-Acr/Ag85B also induced T cell responses in the lung tissues, the primary site of infection, and inhibited bacterial growth in both the lungs and spleens following aerosol challenge with Mtb. DNA-launched Vrep may, therefore, represent an effective approach to the development of gene-based vaccines against TB, particularly as components of heterologous prime-boost strategies or as BCG boosters.  相似文献   
5.
6.
7.
We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1 complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1 PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10-day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02 microgram/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71-86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1-100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.  相似文献   
8.
9.
A new assay procedure for phenol sulfotransferase which employs [35S]-3'-phosphoadenosine-5'-phosphosulfate as a sulfate donor and a variety of phenols as sulfate acceptors was developed. The appearance of the 35S-sulfated products or the disappearance of the [35S]-3'-phosphoadenosine-5'-phosphosulfate are determined simultaneously by chromatography of the assay incubation mixtures on Ecteola-cellulose columns, eluting with an NH4HCO3 step gradient. Various acidic, neutral, and basic phenols can be employed as substrates for phenol sulfotransferase using this procedure.  相似文献   
10.
This article describes the calibration of a spectroscopic scanning instrument for the measurement of selected contaminants in a complex biological process stream. Its use is for the monitoring of a process in which contaminants are to be removed selectively by flocculation from yeast cell homogenate. The main contaminants are cell debris, protein, and RNA. A low-cost instrument has been developed for sensitivity in the region of the NIR spectrum (from 1900 to 2500 nm) where preliminary work found NIR signatures from cell debris, protein, and RNA. Calibration models have been derived using a multivariate method for concentrations of these contaminants, such as would be found after the flocculation process. Two strategies were compared for calibrating the NIR instrument. In one case, samples were prepared by adding materials representative of the contaminants to clarified yeast homogenate so the contaminant levels were well known but outside the range of interest. In the other case, where samples were like those from the process stream after flocculation and floc removal, there was uncertainty of analysis of contaminant level, but the calibration was in the range of interest. Calibration using process stream samples gave results close to those derived from traditional assays. When the calibration models were used to predict the contaminant concentrations in previously unseen samples, the correlation coefficients between measurements and predictions were above 90% in all cases but one. The prediction errors were similar to the errors in the traditional assays.  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