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   5112篇
  免费   418篇
  国内免费   283篇
  2024年   6篇
  2023年   51篇
  2022年   73篇
  2021年   119篇
  2020年   108篇
  2019年   170篇
  2018年   149篇
  2017年   144篇
  2016年   126篇
  2015年   138篇
  2014年   297篇
  2013年   323篇
  2012年   238篇
  2011年   239篇
  2010年   230篇
  2009年   260篇
  2008年   279篇
  2007年   255篇
  2006年   254篇
  2005年   202篇
  2004年   198篇
  2003年   189篇
  2002年   156篇
  2001年   115篇
  2000年   91篇
  1999年   122篇
  1998年   101篇
  1997年   98篇
  1996年   75篇
  1995年   110篇
  1994年   99篇
  1993年   84篇
  1992年   87篇
  1991年   60篇
  1990年   72篇
  1989年   54篇
  1988年   43篇
  1987年   47篇
  1986年   29篇
  1985年   56篇
  1984年   68篇
  1983年   61篇
  1982年   56篇
  1981年   25篇
  1980年   18篇
  1979年   17篇
  1978年   8篇
  1977年   6篇
  1976年   3篇
  1975年   2篇
排序方式: 共有5813条查询结果,搜索用时 15 毫秒
71.
The home range ofTakydromus tachydromoides was studied in a grassland area from April 1977 to November 1978. The mean size of home range did not differ markedly between sexes; 136.5 m2 for males and 130.8 m2 for females. Home ranges of adults overlapped greatly in each sex, and the lizard was considered to be non-territorial. Individuals showed return movement to a definite area (sleeping site) within the home range, and the home range did not shift within a year or between years. Characteristics of the home range of this grassland-inhabiting lizard were discussed in relation to resource abundance and predation pressure.  相似文献   
72.
The binding parameters of the oligomycin-sensitivity conferring protein (OSCP) in inside-out particles from beef heart mitochondria have been tested by means of two assays, the oligomycin-sensitive ATP-Pi exchange, and the oligomycin-sensitive ATP hydrolysis. The total number of OSCP binding sites in A particles was equal to 220 pmol/mg particle protein. Each mole of ATPase active site was able to bind 1.1 +/- 0.5 mol OSCP with Kd 1.7 nM.  相似文献   
73.
A comparison of specific antibodies induced by unfolded actins modified either by oxidation or by arylation of lysine residues was reported. We have focused our work on binding properties with filamentous actin and located its preferential antigenic sites for the anti-arylated-actin antibodies in the C-part of the molecule. An interference of anti-oxidized actin antibodies upon actin polymerisation has also been reported.  相似文献   
74.
Summary The recombination fraction between the interstitially located gene an and interchange 303 of rye was found to be 0.244±0.038 in a test cross using the translocation as the male parent. In first metaphase translocation configurations in pollen mother cells of the same plant, the chiasma frequency between an and the translocation breakpoint was found to be significantly more than twice the recombination fraction. Recombination was concluded to be masked by a difference in the alternate frequency between configurations without interstitial chiasmata and configurations with interstitial chiasmata, the effect of the first type being of major importance. Random centromere orientation of translocation multivalents with interstitial chiasmata was concluded to be a realistic assumption. The exceptionally high recombination between an and translocation 303 is discussed. Consideration is also given to the use of interchanges in the establishment of a marker's chromosomal position, and to the use of translocation chromosomes in balanced systems for hybrid breeding purposes.  相似文献   
75.
The site specificity of the apicomplexans Gregarina cuneata and Gregarina sleini , in larval Tenebrio molitor was investigated. Gregarina cuneata was found to inhabit the anteriormost region of the larval midgut, while G. steini was restricted to the posterior portion of the intestine. The site specificity of the pair was conserved in single and concurrent infections. Interspecific interactions do not seem to be presently responsible for the resource partitioning by the 2 gregarine species. Key words. Gregarina, site specificity, Tenebrio molitor.  相似文献   
76.
Diurnal and seasonal haul-out patterns, site fidelity and activity budgets of individually identified Hooker's sea lions were studied for two years at Papanui Beach, Otago Peninsula, New Zealand.
Fourteen male sea lions were identified. Lengths ranged from 1.65 m–2.28 m and estimated ages from 2-11 yr. The population consisted of four sexually and socially mature (potentially breeding), eight sexually mature but socially immature and two immature males. Most haul-outs (95.6%) were by nine identifiable individuals (Residents) returning on a regular basis, suggesting a high degree of site specificity. Emigration and recruitment were low in relation to the length of the study. Daily arrivals (mean = 0844 h, SD = 1.49) and departures (mean = 1802 h, SD = 1.18) indicate nocturnal feeding. During March 1986 sea lions spent 43.8% of each day ashore (= 78% of daylight hours). Numbers of sea lions hauled out declined in both breeding seasons; in 1986/87 this was due to a decrease in haul-out frequency of resident animals. All but one of these sea lions returned after the breeding season.
Sea lions preferentially selected the middle and the extreme ends of the beach as haul-out sites. During winter use was made of the grass dunes as haul-out areas.
There were significant differences in the frequencies of behavioral activities between summer and winter; more time was allocated to resting in summer.  相似文献   
77.
Muscarinic acetylcholine receptors purified from porcine cerebra or atria were covalently labeled with [3H]propylbenzilylcholine mustard ([3H]PrBCM), and then the labeled receptors were subjected to limited hydrolysis with trypsin, V8 protease, and lysyl endopeptidase, followed by analysis involving sodium dodecyl sulfate-polyacrylamide gel electrophoresis, fluorography, autoradiography, or immunostaining. The labeled peptides were located on the basis of their reactivity with antibodies raised against three synthetic peptides with partial sequences of the m1 or m2 receptor, and of their sensitivity to endoglycosidase F, which was taken as evidence that they contain glycosylation sites near the N terminus. The [3H]PrBCM-binding site in both cerebral and atrial receptors was found to be located between the N terminus and the second intracellular loop, because the size of the smallest deglycosylated peptide that contained both the [3H]PrBCM-binding and glycosylation sites was approximately 16 kDa. Cerebral receptors were 32P-phosphorylated with protein kinase C, and the major phosphorylation sites in cerebral muscarinic receptors were found to be located in a C-terminal segment including a part of the third intracellular loop, because a 32P-labeled peptide of 12-14 kDa reacted with anti-(m1 C-terminal peptide) antiserum. The presence of an intramolecular disulfide bond, probably between Cys 98 and Cys 178 in the first and second extracellular loops, respectively, was suggested by the finding that a peptide of approximately 17 kDa containing the [3H]PrBCM-binding site, but not the glycosylation sites, was partly converted to a peptide of approximately 12 kDa on treatment with beta-mercaptoethanol.  相似文献   
78.
Summary We have determined the DNA sequence of a BALB/cTla region class I gene from the major histocompatibility complex (MHC) that had been identified previously as encoding a murine antigen by DNA-mediated gene transfer. Analysis of the DNA sequence shows, however, that this gene, the T1c gene from theTla c genotype, could not encode a TL antigen or any other functional class I molecule due to the presence of numerous stop codons and frameshift mutations in the coding regions. This result suggests that the earlier transformation data may have been incorrect or perhaps that the clone containing the T1c gene contains sequences that induced expression of a serologically reactiveTla gene in the genome of the recipient L cell. The T1c gene is structurally related to the previously sequenced T13c gene that encodes a serologically defined TL antigen. The 3 half of the T1c gene including exons 4, 5, 6, and the 3 untranslated region has about 85% nucleotide similarity (including introns) with the corresponding parts of the T13c gene; however, the 5 half of the T1c gene has little homology with the T13c gene. There is a sharp line of demarcation between the homologous and nonhomologous regions, and this border occurs precisely at a B2 Alu repeat sequence present in the T13c gene. This suggests that a recombination event took place here and that an Alu repeat sequence that is known to have characteristics of transposable elements played some role in a recombination or gene conversion event.  相似文献   
79.
Summary We have devised a method whereby any mutagenized cloned DNA from Bacillus subtilis can be reinserted at the original site on the B. subtilis chromosome. The procedure depends on the accuracy and high frequency of homologous recombination between the B. subtilis chromosome and the DNA taken up by the cell. The method makes use of two drug resistance selection markers (the chloramphenicol resistance gene and the neomycin resistance gene) and a marker gene which functions as a catalyst. The utility of the method has been demonstrated using leuB and pro of B. subtilis as target gene and catalyst, respectively, and mutations such as leuB: : cat, leuB , and pro: : neo constructed in vitro on the cloned DNA fragments. Transformation in sequential steps as (leuB + pro+)(leuB: : cat pro +) (leuB pro: : neo)(leuB pro +) resulted in a leuB single mutant without affecting other regions of the B. subtilis chromosome (gene-directed mutagenesis). We also demonstrate that other single mutations such as metD and pro , as well as the double mutation leuB pro can be introduced by the same procedure. In principle, true isogenies with multiple mutations can be constructed by the method described in this paper. Furthermore, the procedure should be generally applicable to any organisms in which homologous recombination is proficient.  相似文献   
80.
Summary A generally applicable method is described for reintroduction of mutant plasmid-borne alleles to the chromosome of Klebsiella pneumoniae using bacteriophage . We, used this method to make stable chromosomal transposon insertions in genes for biosynthesis of pyrroloquinoline quinone in K. pneumoniae  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