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   2922篇
  免费   235篇
  3157篇
  2024年   3篇
  2023年   18篇
  2022年   44篇
  2021年   68篇
  2020年   47篇
  2019年   72篇
  2018年   95篇
  2017年   59篇
  2016年   105篇
  2015年   172篇
  2014年   173篇
  2013年   227篇
  2012年   279篇
  2011年   265篇
  2010年   141篇
  2009年   135篇
  2008年   169篇
  2007年   162篇
  2006年   144篇
  2005年   109篇
  2004年   119篇
  2003年   124篇
  2002年   96篇
  2001年   31篇
  2000年   29篇
  1999年   32篇
  1998年   33篇
  1997年   28篇
  1996年   23篇
  1995年   14篇
  1994年   17篇
  1993年   12篇
  1992年   24篇
  1991年   14篇
  1990年   7篇
  1989年   7篇
  1988年   3篇
  1987年   6篇
  1985年   8篇
  1984年   2篇
  1983年   6篇
  1982年   3篇
  1981年   8篇
  1980年   2篇
  1979年   4篇
  1978年   2篇
  1977年   4篇
  1974年   2篇
  1965年   1篇
  1961年   2篇
排序方式: 共有3157条查询结果,搜索用时 15 毫秒
91.
Both dorsal and ventral cortical visual streams contain neurons sensitive to binocular disparities, but the two streams may underlie different aspects of stereoscopic vision. Here we investigate stereopsis in the neurological patient D.F., whose ventral stream, specifically lateral occipital cortex, has been damaged bilaterally, causing profound visual form agnosia. Despite her severe damage to cortical visual areas, we report that DF''s stereo vision is strikingly unimpaired. She is better than many control observers at using binocular disparity to judge whether an isolated object appears near or far, and to resolve ambiguous structure-from-motion. DF is, however, poor at using relative disparity between features at different locations across the visual field. This may stem from a difficulty in identifying the surface boundaries where relative disparity is available. We suggest that the ventral processing stream may play a critical role in enabling healthy observers to extract fine depth information from relative disparities within one surface or between surfaces located in different parts of the visual field.  相似文献   
92.
A software suite KINALYZER reconstructs full-sibling groups without parental information using data from codominant marker loci such as microsatellites. KINALYZER utilizes a new algorithm for sibling reconstruction in diploid organisms based on combinatorial optimization. KINALYZER makes use of a Minimum 2-Allele Set Cover approach based on Mendelian inheritance rules and finds the smallest number of sibling groups that contain all the individuals in the sample. Also available is a 'Greedy Consensus' approach that reconstructs sibgroups using subsets of loci and finds the consensus of the partial solutions. Unlike likelihood methods for sibling reconstruction, KINALYZER does not require information about population allele frequencies and it makes no assumptions regarding the mating system of the species. KINALYZER is freely available as a web-based service.  相似文献   
93.
Lung cancer is the leading cause of cancer-related death. Despite a number of studies that have provided prognostic biomarkers for lung cancer, a paucity of reliable markers and therapeutic targets exist to diagnose and treat this aggressive disease. In this study we investigated the potential of nuclear receptors (NRs), many of which are well-established drug targets, as therapeutic markers in lung cancer. Using quantitative real-time PCR, we analyzed the expression of the 48 members of the NR superfamily in a human panel of 55 normal and lung cancer cell lines. Unsupervised cluster analysis of the NR expression profile segregated normal from tumor cell lines and grouped lung cancers according to type (i.e. small vs. non-small cell lung cancers). Moreover, we found that the NR signature was 79% accurate in diagnosing lung cancer incidence in smokers (n = 129). Finally, the evaluation of a subset of NRs (androgen receptor, estrogen receptor, vitamin D receptor, and peroxisome proliferator-activated receptor-γ) demonstrated the therapeutic potential of using NR expression to predict ligand-dependent growth responses in individual lung cancer cells. Preclinical evaluation of one of these receptors (peroxisome proliferator activated receptor-γ) in mouse xenografts confirmed that ligand-dependent inhibitory growth responses in lung cancer can be predicted based on a tumor's receptor expression status. Taken together, this study establishes NRs as theragnostic markers for predicting lung cancer incidence and further strengthens their potential as therapeutic targets for individualized treatment.  相似文献   
94.
Three new triterpenoids, including two rare D:B-friedobaccharanes (leonatriol, 1 and leonatriolone, 2) and a 2,3-seco-2,24-epoxy-3,24-olide-D:A-friedooleanane (cassinolide, 3) were isolated from the root bark of Cassine xylocarpa and Celastrus vulcanicola, collected in El Salvador. Their stereostructures were elucidated on the basis of spectroscopic analyses, mainly 1D and 2D NMR techniques, spectrometric analyses, and comparison with data reported in the literature. The absolute configuration of 1 and 2 were determined by the application of the Riguera ester procedure and biogenetic considerations. The possible biogenetic pathway for cassinolide (3) is also discussed.  相似文献   
95.
96.
A linear model and three nonlinear models (Logan type III, Lactin and Brière) were applied to Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) at constant temperatures and validated under diel temperature variation, and field conditions. Complete development from egg to adult, with >80% survivorship, occurred at nine constant temperatures between 15 and 32 °C. Total developmental time decreased from a maximum at 15 °C (68.48 days) to a minimum at 30 °C (18.69 days) and then increased at 32 °C (23.44 days). Optimal survival and the highest developmental rate occurred within the range of 27–30 °C. The adjusted determination coefficients were high for linear and nonlinear models (>0.89). Field validation showed high levels of accuracy in all models (≥93.4%). These valid mathematical models contribute to optimal application, field management, and mass rearing of M. pygmaeus for its applicability to biological control.  相似文献   
97.
Lophodermium comprises ascomycetous fungi that are both needle-cast pathogens and asymptomatic endophytes on a diversity of plant hosts. It is distinguished from other genera in the family Rhytismataceae by its filiform ascospores and ascocarps that open by a longitudinal slit. Nucleotide sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA were used to infer phylogenetic relationships within Lophodermium. Twenty-nine sequences from approximately 11 species of Lophodermium were analyzed together with eight sequences from isolates thought to represent six other genera of Rhytismataceae: Elytroderma, Lirula, Meloderma, Terriera, Tryblidiopsis and Colpoma. Two putative Meloderma desmazieresii isolates occurred within the Lophodermium clade but separate from one another, one grouped with L. indianum and the other with L. nitens. An isolate of Elytroderma deformans also occurred within the Lophodermium clade but on a solitary branch. The occurrence of these genera within the Lophodermium clade might be due to problems in generic concepts in Rhytismataceae, such as emphasis on spore morphology to delimit genera, to difficulty of isolating Rhytismataceae needle pathogens from material that also is colonized by Lophodermium or to a combination of both factors. We also evaluated the congruence of host distribution and several morphological characters on the ITS phylogeny. Lophodermium species from pine hosts formed a monophyletic sister group to Lophodermium species from more distant hosts from the southern hemisphere, but not to L. piceae from Picea. The ITS topology indicated that Lophodermium does not show strict cospeciation with pines at deeper branches, although several closely related isolates have closely related hosts. Pathogenic species occupy derived positions in the pine clade, suggesting that pathogenicity has evolved from endophytism. A new combination is proposed, Terriera minor (Tehon) P.R. Johnst.  相似文献   
98.
99.
We employed a prime-boost regimen in combination with the expression library immunization protocol to improve the protective effectiveness of a genomic library used as immunogen. To demonstrate the feasibility of this novel strategy, we used as a prime a serogroup B Neisseria meningitidis random genomic library constructed in a eukaryotic expression vector. Mice immunized with different fractions of this library and boosted with a single dose of meningococcal outer membrane vesicles elicited higher bactericidal antibody titers compared with mice primed with the empty vector. After the boost, passive administration of sera from mice primed with two of these fractions significantly reduced the number of viable bacteria in the blood of infant rats challenged with live N. meningitidis. The method proposed could be applied to the identification of subimmunogenic antigens during vaccine candidate screening by employing expression library immunization.  相似文献   
100.
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