全文获取类型
收费全文 | 34341篇 |
免费 | 2869篇 |
国内免费 | 1825篇 |
出版年
2023年 | 332篇 |
2022年 | 382篇 |
2021年 | 1580篇 |
2020年 | 1032篇 |
2019年 | 1250篇 |
2018年 | 1225篇 |
2017年 | 864篇 |
2016年 | 1327篇 |
2015年 | 2028篇 |
2014年 | 2373篇 |
2013年 | 2559篇 |
2012年 | 3088篇 |
2011年 | 2771篇 |
2010年 | 1720篇 |
2009年 | 1434篇 |
2008年 | 1669篇 |
2007年 | 1519篇 |
2006年 | 1356篇 |
2005年 | 1145篇 |
2004年 | 1023篇 |
2003年 | 866篇 |
2002年 | 744篇 |
2001年 | 677篇 |
2000年 | 681篇 |
1999年 | 655篇 |
1998年 | 386篇 |
1997年 | 325篇 |
1996年 | 351篇 |
1995年 | 333篇 |
1994年 | 325篇 |
1993年 | 217篇 |
1992年 | 351篇 |
1991年 | 270篇 |
1990年 | 305篇 |
1989年 | 257篇 |
1988年 | 190篇 |
1987年 | 170篇 |
1986年 | 152篇 |
1985年 | 134篇 |
1984年 | 121篇 |
1983年 | 95篇 |
1982年 | 77篇 |
1981年 | 60篇 |
1980年 | 45篇 |
1979年 | 74篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1975年 | 59篇 |
1974年 | 47篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Plants contain highly divergent actin isovariants 总被引:5,自引:0,他引:5
B G McLean S R Huang E C McKinney R B Meagher 《Cell motility and the cytoskeleton》1990,17(4):276-290
Actin protein isovariants have been identified in animals with distinct cytoplasmic or muscle specific patterns of expression. Analysis of vascular plant actin gene sequences suggests that an even greater diversity should exist within the plant actin protein families, but previous studies on plant proteins have not demonstrated the presence of multiple actin isovariants. Antibodies recognizing a conserved amino-terminal plant actin peptide, a family of plant actin peptides from a variable region, and two monoclonal antibodies to conserved epitopes within animal actins were used to identify isovariants of soybean actin resolved by two-dimensional isoelectric focusing (IEF) sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Approximately six to eight actin isovariants with pI values ranging from 5.1 to 5.8 have been identified from soybean hypocotyls, stems, leaves, and roots with varying amounts of most isovariants present in all four organs. Acidic isovariants were present in much higher levels in leaves and stems. Antisera with lambda-class actin specificity detected a subset of three isovariants in all organs examined. One monoclonal and one antipeptide antisera are shown to react well with a wide variety of plant actin isovariants. Similar patterns of actin isovariants were detected in the distant angiosperms, Arabidopsis, petunia, and maize. It is likely that many of these diverse classes of isovariants have been preserved throughout vascular plant evolution and reflect the ancient diversity within plant actin gene families. The extreme difference among isovariants implies the presence of a complex actin-based cytoskeletal system in plants. 相似文献
102.
103.
D A Compton M M Weil L Bonetta A Huang C Jones H Yeger B R Williams L C Strong G F Saunders 《Genomics》1990,6(2):309-315
In a previous report, we described a contiguous restriction map of chromosome band 11p13 that localized the Wilms tumor locus to a small group of NotI fragments. In an effort to identify and isolate the 11p13-associated sporadic Wilms tumor locus, we developed a panel of NotI fragment-specific DNA probes. These probes were selected from genomic libraries constructed using the Chinese hamster ovary-human somatic cell hybrid carrying only human 11p. The libraries were prepared from NotI-digested DNA after size selection by pulsed-field gel electrophoresis. The selected NotI fragments had been previously targeted on the basis of deletion mapping as having a high probability of containing the Wilms tumor locus. We used these newly identified 11p13-specific probes to improve the resolution of the restriction map spanning the Wilms tumor locus. The locus has been defined by a homozygous deletion in a sporadic Wilms tumor. Using these probes, the region of homozygous deletion in this tumor and presumably all or part of the Wilms tumor gene have been confined to two small SfiI fragments spanning less than 350 kb. 相似文献
104.
本文记述了在云南省建水县岔科地区发现的哺乳动物化石。根据豫鼠(Yuomys),定地层时代为晚始新世。这套地层暂称岔科组,以示滇南地区第一个含早第三纪哺乳动物的地点和层位。 相似文献
105.
桂西壮族手皮纹的分析 总被引:4,自引:0,他引:4
本文对广西西部500例健康壮族大、中学生的手皮纹进行了观察分析,计算出各型指纹频率、指纹脊线总数、指纹频度指数、atd角度、a-b脊线数、τ距比、主线横向指数、皮纹花样出现率、掌褶纹出现率共九项基本参数,并将这些数值与汉族作了比较,桂西壮族的手纹与汉族既有相似之处,又有本民族的特点。 相似文献
106.
Physical identification of branched intron side-products of splicing in Trypanosoma brucei. 总被引:9,自引:2,他引:7
Every mRNA in trypanosomes consists of two exons, a common 5' capped mini-exon or spliced leader and a coding-exon. All evidence suggests that the exons are joined by trans-splicing of two individual precursor RNAs, the mini-exon donor RNA or spliced leader precursor RNA (medRNA) and the pre-mRNA. We studied intermediates of the splicing reaction using denaturing two-dimensional PAGE and structurally identified a group of small (approximately 180-300 nt) non-polyadenylated, Y-shaped branched RNAs. The branched Y-shaped RNAs contain the 105 nt medRNA derived intron, joined in a 2'-5' phosphodiester bond to small heterogeneously sized RNAs. These non-polyadenylated branched Y-shaped RNA molecules are analogous to the lariat shaped introns of higher eukaryotes and presumably represent the released intron-like by-products of a trans-splicing reaction which joins the mini-exon and the major coding-exon. 相似文献
107.
The lactose plasmid pUCL22 of the single plasmid strain Streptococcus lactis ssp. lactis Z270 was demonstrated to fuse with the heterologous conjugative plasmid pVA797. The fusion of pUCL22 with pVA797 occurred by recombination between a specific sequence of pUCL22 and different sites of pVA797. The cointegrates of pUCL22::pVA797 were unstable: in the absence of lactose selection, they segregated plasmids that corresponded to pVA797 enlarged by one sequence of 1.2 kb, common to all derivative plasmids. This resolution sequence (RS) was shown to originate in the 9.7 kb BstEII restriction fragment of pUCL22 and to duplicate during replicon fusion. In addition, after nuclease S1 treatment of pUCL22 DNA, a self-annealing sequence was isolated; the two copies of this inverted repeat (IR) sequence were located on the 18 kb BamHI segment of the plasmid. This latter sequence was distinct from the RS with which it hybridized weakly. The RS was responsible for the transposition of the entire lactose plasmid; the role of the IR remains to be elucidated. 相似文献
108.
109.
Incubation of rat brain synaptosomes prelabeled with [2-3H]inositol resulted in a time-dependent release of labeled inositol 1-phosphate. This process was Ca2+ dependent, and ATP (1 mM) enhanced the inositol 1-phosphate formation three- to fivefold. Using [1-14C]arachidonoyl-phosphatidylinositol which was introduced into saponin-permeabilized synaptosomes, ATP (1 mM) and free Ca2+ (approximately 20 microM) enhanced the phospholipase C hydrolysis of this substrate to form labeled diacylglycerol. When the same permeabilized synaptosomal preparation was incubated with [2-3H]inositol-phosphatidylinositol, ATP not only enhanced the formation of labeled inositol 1-phosphate, but also inhibited the conversion of inositol 1-phosphate to inositol. Furthermore, ATP appeared to reduce the Ca2+ requirement of the phosphatidylinositol-phospholipase C. Inhibition of the conversion of inositol 1-phosphate to inositol could not be overcome by increasing the Mg2+ concentration in the incubation medium. Although the ATP effect is not viewed as a receptor-mediated event, it is possible that such an event may occur in synaptosomes under conditions in which intrasynaptic Ca2+ concentration becomes elevated. 相似文献
110.