全文获取类型
收费全文 | 762162篇 |
免费 | 85458篇 |
国内免费 | 334篇 |
专业分类
847954篇 |
出版年
2018年 | 6710篇 |
2016年 | 9076篇 |
2015年 | 12079篇 |
2014年 | 14225篇 |
2013年 | 20444篇 |
2012年 | 22924篇 |
2011年 | 23428篇 |
2010年 | 15960篇 |
2009年 | 14855篇 |
2008年 | 21383篇 |
2007年 | 21965篇 |
2006年 | 20838篇 |
2005年 | 19860篇 |
2004年 | 19820篇 |
2003年 | 18907篇 |
2002年 | 18522篇 |
2001年 | 32094篇 |
2000年 | 32218篇 |
1999年 | 26241篇 |
1998年 | 9555篇 |
1997年 | 9966篇 |
1996年 | 9498篇 |
1995年 | 8714篇 |
1994年 | 8728篇 |
1993年 | 8674篇 |
1992年 | 22056篇 |
1991年 | 21515篇 |
1990年 | 21238篇 |
1989年 | 20913篇 |
1988年 | 19558篇 |
1987年 | 18704篇 |
1986年 | 17380篇 |
1985年 | 17405篇 |
1984年 | 14390篇 |
1983年 | 12605篇 |
1982年 | 9698篇 |
1981年 | 8641篇 |
1980年 | 8356篇 |
1979年 | 13964篇 |
1978年 | 10953篇 |
1977年 | 9898篇 |
1976年 | 9569篇 |
1975年 | 10337篇 |
1974年 | 11269篇 |
1973年 | 11076篇 |
1972年 | 10197篇 |
1971年 | 9200篇 |
1970年 | 8093篇 |
1969年 | 7789篇 |
1968年 | 7274篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
183.
184.
185.
Samples of marine pleuston were collected from the sea-surface along considerable sections of the track of Eye of the Wind during its 2-year circumnavigational expedition 'Operation Drake' from November 1978 to October 1980. One hundred and eleven of the tow samples contained insects of the genus Halobates . They were assigned to four oceanic species: H. micans, H. sericeus, H. germanus and H. splendens; two coastal species: H. maculatus, H. princeps, and one undescribed species. Various development stages of the oceanic species were found. The locations, time of collection and surface temperatures where sea-skaters were collected are tabulated. Distributional boundaries and population densities of the oceanic species collected are discussed. 相似文献
186.
Ffh is a component of a bacterial ribonucleoprotein complex homologous to the signal recognition particle (SRP) of eukaryotes. It comprises three domains that mediate both binding to the hydrophobic signal sequence of the nascent polypeptide and the GTP-dependent interaction of Ffh with a structurally homologous GTPase of the SRP receptor. The X-ray structures of the two-domain 'NG' GTPase of Ffh in complex with Mg2+GDP and GDP have been determined at 2.0 A resolution. The structures explain the low nucleotide affinity of Ffh and locate two regions of structural mobility at opposite sides of the nucleotide-binding site. One of these regions includes highly conserved sequence motifs that presumably contribute to the structural trigger signaling the GTP-bound state. The other includes the highly conserved interface between the N and G domains, and supports the hypothesis that the N domain regulates or signals the nucleotide occupancy of the G domain. 相似文献
187.
E Giannazzo F Licata G Li Volsi G Mio F Santangelo M Scivoli 《Bollettino della Società italiana di biologia sperimentale》1992,68(11):677-683
A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus. 相似文献
188.
1L-myo-Inositol-1-phosphatase, an enzyme purified from brain tissues, catalyzes the dephosphorylation of 1L-myo-inositol 1-phosphate. This enzyme has become the subject of intense research interest, since myo-inositol is needed for the resynthesis of phosphatidylinositol. We have developed a sensitive fluorometric assay for detecting the activity of 1L-myo-inositol-1-phosphatase. The assay is based on o-aminobenzoyl beta-glycerophosphate fluorescence, according to the following principles: (I) The fluorescence yield of o-aminobenzoyl beta-glycerophosphate is increased by 2.75-fold in the presence of saturating concentrations of bovine serum albumin. (II) o-Aminobenzoyl beta-glycerophosphate has the same fluorescence yield as o-aminobenzoyl glycerol, but the latter does not bind to bovine serum albumin. (III) Dephosphorylation of the substrate, catalyzed by the monophosphatase, makes less o-aminobenzoyl beta-glycerophosphate available for binding to bovine serum albumin, thereby producing a decrease in the fluorescence intensity. 相似文献
189.
Cynthia L. Deitrick Richard E. Katholi David J. Huddleston Kathy Hardiek Lucienne Burrus 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2001,751(2)
Vitamin B6, measured as pyridoxal 5′-phosphate (PLP), is a co-enzyme in the transsulfuration pathway of homocysteine metabolism. Since depletion of PLP has been suggested as an independent risk factor for coronary artery disease, PLP is frequently measured to guide patient care. By a change and utilization of an Aquasil C18 column and the addition of an acetonitrile clean-up gradient to the potassium phosphate, with sodium perchlorate and bisulfite buffer between samples we report the modification of a previously described method for analysis of PLP. The result is a more practical, efficient, reliable and robust method for daily clinical use. We also determined and report that it is critical to protect freshly prepared standard PLP samples from light exposure during assay preparation. 相似文献
190.