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   2465篇
  免费   157篇
  2022年   10篇
  2021年   39篇
  2020年   10篇
  2019年   17篇
  2018年   35篇
  2017年   31篇
  2016年   46篇
  2015年   67篇
  2014年   68篇
  2013年   144篇
  2012年   105篇
  2011年   124篇
  2010年   79篇
  2009年   98篇
  2008年   144篇
  2007年   163篇
  2006年   130篇
  2005年   140篇
  2004年   140篇
  2003年   159篇
  2002年   137篇
  2001年   53篇
  2000年   57篇
  1999年   57篇
  1998年   28篇
  1997年   24篇
  1996年   12篇
  1995年   27篇
  1994年   28篇
  1993年   21篇
  1992年   33篇
  1991年   39篇
  1990年   37篇
  1989年   37篇
  1988年   21篇
  1987年   21篇
  1986年   20篇
  1985年   23篇
  1984年   14篇
  1983年   16篇
  1981年   14篇
  1980年   10篇
  1978年   12篇
  1976年   9篇
  1975年   14篇
  1974年   13篇
  1973年   13篇
  1972年   9篇
  1971年   11篇
  1967年   9篇
排序方式: 共有2622条查询结果,搜索用时 62 毫秒
41.
We have reported the isolation of linking clones of HindIII and EcoRI fragments, altogether spanning a 230-kb continuous stretch of chromosome VI. The presence or absence of autonomously replicating sequence (ARS) activities in all of these fragments has been determined by using ARS searching vectors containing CEN4. Nine ARS fragments were identified, and their positions were mapped on the chromosome. Structures essential for and/or stimulative to ARS activity were determined for the ARS fragments by deletions and mutations. The organization of functional elements composed of core and stimulative sequences was found to be variable. Single core sequences were identified in eight of nine ARSs. The remaining ARS (ARS603) essential element is composed of two core-like sequences. The lengths of 3'- and 5'-flanking stimulative sequences required for the full activity of ARSs varied from ARS to ARS. Five ARSs required more than 100 bp of the 3'-flanking sequence as stimulative sequences, while not more than 79 bp of the 3' sequence was required by the other three ARSs. In addition, five ARSs had stimulative sequences varying from 127 to 312 bp in the 5'-flanking region of the core sequence. In general, these stimulative activities were correlated with low local delta Gs of unwinding, suggesting that the low local delta G of an ARS is an important element for determining the efficiency of initiation of replication of ARS plasmids.  相似文献   
42.
Individual differences in sensitivity to bitter-tasting substances   总被引:4,自引:4,他引:0  
Perception of several bitter-tasting compounds was tested in52 subjects. Stable individual differences in the perceivedintensity of the bitterness of suprathreshold concentrationsof quinine sulfate (QSO4) and urea were found. Whereas 18 subjectsjudged selected concentrations of these compounds to be equallybitter, 17 found QSO4 to be more bitter than urea, and 17 foundurea to be more bitter than QSO4. These reliable individualdifferences were significantly related to threshold sensitivityto QSO4; that is, individuals who perceived QSO4 to be moreintense than urea at suprathreshold concentrations also hadlower QSO4 thresholds than did those who perceived urea to bemore intense than QSO4. There appeared to be no relationshipbetween the relative perceived intensities of these compoundsand rating of the bitterness of PROP (6-n-propylthiouracil).However, QSO4-sensitive individuals tended to find the bitternessof suprathreshold caffeine and sucrose octaacetate to be greaterthan that of suprathreshold magnesium sulfate, whereas the reversewas true for urea-sensitive individuals. This pattern parallelsthe pattern of cross-adaptation among these compounds reportedby other investigators. These results are consistent with theexistence of multiple bitter transduction sequences and suggestthat individual differences in response to various bitter compoundsmay reflect differences in teh relative availability of specifictransduction sequences.  相似文献   
43.
Journal of Plant Research - A group of temperate grassland plant species termed the “Mansen elements” occurs in Japan and is widely distributed in the grasslands of continental East...  相似文献   
44.
Human liver guanase was purified and a specific antibody against it was raised in rabbits. The antiserum formed a single precipitin line with human liver extract, and also completely inhibited the activity of the liver enzyme. An immunoblotting study showed that the antibody bound specifically to one band of protein with guanase activity and not to other proteins. Therefore, we concluded that this antiserum against the liver enzyme was suitable for use in immunohistochemical demonstration of guanase. In tissue sections, the immunohistochemical reaction with this antibody was positive in the same locations as the histochemical guanase reaction with DAB (3,3'-diaminobenzidine tetrahydrochloride).  相似文献   
45.
Occupational or recreational exercise reduces mortality from cardiovascular disease. The potential mechanisms for this reduction may include changes in blood pressure (BP) and autonomic control of the circulation. Therefore, we conducted the present long-term longitudinal study to quantify the dose-response relationship between the volume and intensity of exercise training, and regulation of heart rate (HR) and BP. We measured steady-state hemodynamics and analyzed dynamic cardiovascular regulation by spectral and transfer function analysis of cardiovascular variability in 11 initially sedentary subjects during 1 yr of progressive endurance training sufficient to allow them to complete a marathon. From this, we found that 1) moderate exercise training for 3 mo decreased BP, HR, and total peripheral resistance, and increased cardiovascular variability and arterial baroreflex sensitivity; 2) more prolonged and intense training did not augment these changes further; and 3) most of these changes returned to control values at 12 mo despite markedly increased training duration and intensity equivalent to that routinely observed in competitive athletes. In conclusion, increases in R-wave-R-wave interval and cardiovascular variability indexes are consistent with an augmentation of vagal modulation of HR after exercise training. It appears that moderate doses of training for 3 mo are sufficient to achieve this response as well as a modest hypotensive effect from decreasing vascular resistance. However, more prolonged and intense training does not necessarily lead to greater enhancement of circulatory control and, therefore, may not provide an added protective benefit via autonomic mechanisms against death by cardiovascular disease.  相似文献   
46.
A new mode of herbicidal action was established by finding specific inhibitors of imidazoleglycerol phosphate dehydratase, an enzyme of histidine (His) biosynthesis. Three triazole phosphonates inhibited the reaction of the enzyme with Ki values of 40 [plus or minus] 6.5, 10 [plus or minus] 1.6, and 8.5 [plus or minus] 1.4 nM, respectively, and were highly cytotoxic to cultured plant cells. This effect was completely reversed by the addition of His, proving that the cytotoxicity was primarily caused by the inhibition of His biosynthesis. These inhibitors showed wide-spectrum, postemergent herbicidal activity at application rates ranging from 0.05 to 2 kg/ha.  相似文献   
47.
The anti-HLA-DQ3 monoclonal antibodies (mAb) KS13, SO1, SO2, SO3, SO4, and SO5 recognize spatially close but distinct antigenic determinants, since they crossinhibit each other in their binding to HLA-DQ3 antigens, but do not share idiotopes recognized in their antigen combining site by syngeneic and anti-id antisera and mAb. Furthermore, mAb SO1, SO3, SO4, and SO5 react also with HLA-DQ allospecificities other than HLA-DQ3. Sequence analysis of the heavy (V H ) and light (V L ) chain variable region of the six mAb revealed preferential usage of V H 36–60 and V K 12/13 gene families. However, the individual V H and V L germline gene usage by the six mAb is diverse and the utilization of D, J H , and J L gene segments is heterogeneous. The diverse usage of V H and V L gene segments and heterogeneous amino acid sequences of V H and V L CDR, together with the heterogeneous idiotypic profile, may reflect the complexity of the determinants recognized by the six mAb on HLA-DQ3 antigens. The results we have presented provide for the first time information about the structural basis of the diversity of antibodies recognizing human histocompatibility antigens.The nucleotide sequence data reported in this Papershave been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers L20499, L20957, L20961, L24557, L24558 and L20962, respectively, for V H region genes, and L20956, L20958, L24555, L24556, L20959, and L20960, respectively, for V L region genes  相似文献   
48.
We determined the sequence of the 2,138 nucleotides in the Sendai virus genome just following the 3' proximal 3,686 nucleotides which we had previously reported (Nucleic Acids Res. 11, 7317-7330, 1983). This covers the entire third gene of 1,173 nucleotides and the 3' proximal 1,013 nucleotides of the fourth gene. Like the NP and P+C genes, both the third and fourth genes start from consensus sequence R1 (3'-UCCCAC(or UA)UUUC) at the 3' end and the third gene terminates with consensus sequence R2 (3'-AUUCUUUUU) at the 5' end. The third gene was identified as M, and the deduced 348 amino acids indicated that the M protein is rich in basic residues and has hydrophobic domains near the C-terminal. The fourth gene, although sequencing is not complete yet, was identified as F, since a large open reading frame found in the gene contains the characteristic sequence of 20 amino acids located at the N-terminal of the F1 protein. Analyses of the amino acid sequence suggested that the structure of the F gene product is NH2-signal peptide-F2-F1-COOH.  相似文献   
49.
Terpenoid and acetylenic components not reported previously in Artemisia capillaris have been identified, including p-cymene, 5-phenyl-1, 3-diyne, dehydrofalcarinone and dehydrofalcarinol. The distribution of volatile components in different parts of the plant is described.  相似文献   
50.
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