全文获取类型
收费全文 | 785257篇 |
免费 | 88620篇 |
国内免费 | 891篇 |
专业分类
874768篇 |
出版年
2018年 | 7218篇 |
2016年 | 9819篇 |
2015年 | 13647篇 |
2014年 | 16043篇 |
2013年 | 22028篇 |
2012年 | 25363篇 |
2011年 | 26145篇 |
2010年 | 17697篇 |
2009年 | 16211篇 |
2008年 | 23442篇 |
2007年 | 24346篇 |
2006年 | 22904篇 |
2005年 | 21737篇 |
2004年 | 21858篇 |
2003年 | 20521篇 |
2002年 | 20043篇 |
2001年 | 31717篇 |
2000年 | 31886篇 |
1999年 | 25480篇 |
1998年 | 9606篇 |
1997年 | 9787篇 |
1996年 | 9242篇 |
1995年 | 8824篇 |
1994年 | 8422篇 |
1993年 | 8534篇 |
1992年 | 21425篇 |
1991年 | 21284篇 |
1990年 | 20763篇 |
1989年 | 20085篇 |
1988年 | 19060篇 |
1987年 | 18069篇 |
1986年 | 17027篇 |
1985年 | 16771篇 |
1984年 | 14035篇 |
1983年 | 12241篇 |
1982年 | 9385篇 |
1981年 | 8453篇 |
1980年 | 7968篇 |
1979年 | 13347篇 |
1978年 | 10762篇 |
1977年 | 9703篇 |
1976年 | 9264篇 |
1975年 | 10326篇 |
1974年 | 11457篇 |
1973年 | 11229篇 |
1972年 | 10231篇 |
1971年 | 9434篇 |
1970年 | 8166篇 |
1969年 | 8066篇 |
1968年 | 7550篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
The authors analyze the results of comparative studies on 15 paired sera from children with suspected measles, of 32 sera from children and adolescents aged 1.5 to 16 immunized against measles, and of 21 sera from adults aged 19 to 86 with a history of the disease. EIA proved to be more sensitive than HAIT: the detection rate of positive sera was higher, as were the titers of antibodies detected by it, in examinations of the sera from vaccinated children and the adults. Analysis of the distribution of sera with different titers of antibody to measles virus in EIA and HAIT has revealed a correlation between the titers in the sera with high antibody levels. In the cases with low antihemagglutinin titers, no correlation between the titers determined in the two tests has been observed. 相似文献
993.
G G Hillebrand A H McCluskey K A Abbott G G Revich K L Beattie 《Nucleic acids research》1984,12(7):3155-3171
A method has been developed for simultaneous comparison of the propensity of a DNA polymerase to misincorporate at different points on a natural template-primer. In this method elongation of a [5'-32P] primer, annealed to a bacteriophage template strand, is carried out in the presence of only three dNTPs (highly purified by HPLC). Under these conditions the rate of primer elongation (monitored by gel electrophoresis/autoradiography) is limited by the rate of misincorporation at template positions complementary to the missing dNTP. Variations in the rate of elongation (revealed by autoradiographic banding patterns) reflect variations in the propensity for misincorporation at different positions along the template. The effect on primer elongation produced by addition of a chemically modified dNTP to 'minus' reactions reveals the mispairing potential of the modified nucleotide during DNA synthesis. By use of this electrophoretic assay of misincorporation we have demonstrated that the fidelity of E. coli DNA polymerase I varies greatly at different positions along a natural template, and that BrdUTP and IodUTP can be incorporated in place of dCTP during chain elongation catalyzed by this enzyme. 相似文献
994.
995.
In this study we construct a phylogenetic hypothesis for the relatedness among disjunct subspecies of Cyclamen repandum and its two allopatric congeners, C. creticum and C. balearicum in order to examine the evolutionary divergence of currently isolated populations across the western Mediterranean. The most
parsimonious phylogenetic tree obtained from sequencing the cpDNA trnL (UAA) intron suggests a major phylogeographic divide in southern Greece between two clades. The first clade comprises samples
of C. repandum subsp. peloponnesiacum (from the Peloponnese) and C. creticum (from Crete). The second comprises samples of C. repandum subsp. repandum (from Croatia, Italy, southern France, Corsica, Sardinia and Sicily), C. repandum subsp. rhodense (from Rhodes and Kos) and C. balearicum (from the Balearic Islands and southern France). These data suggest that C. creticum has evolved in allopatry from C. repandum subsp. peloponnesiacum and that C. balearicum and C. repandum ssp. rhodense have diverged from C. repandum subsp. repandum at its western and eastern distribution limits. At one small site on Corsica, a population of C. repandum may have introgressed with relictual populations of C. balearicum. These divergence patterns illustrate how a phylogenetic perspective can be used to better understand the evolution of endemism
in the Mediterranean flora.
Received February 19, 2001 Accepted August 22, 2001 相似文献
996.
Characterization of a novel kinetochore protein, CENP-H. 总被引:11,自引:0,他引:11
997.
Vrieling E. G. Gieskes W. W.C. Beelen T. P. M. & van Santen R.A. 《Journal of phycology》2000,36(S3):70-70
Using a high-brilliance synchrotron X-ray source, combined small- and wide-angle X-ray scattering (SAXS and WAXS) was applied to study nanoscale characteristics, in particular pore size in the range of 3 to 65 nm, of a variety of unialgal cultures of centric and pennate diatoms, and of mixed diatom populations sampled in the field. Results of scattering analysis were compared with details of pore size, structure and orientation visible at the electron microscopic level. WAXS patterns did not reveal any crystalline phase or features of microcrystallinity (resolution 0.07 to 0.51 nm), which implies a totally amorphous character of the SiO2 matrix of the frustule material. SAXS data (resolution 3 to 65 nm) provided information on geometry, size, and distribution of pores in the silica. Overall, two pore regions were recognized that were common to the silica of all samples: the smallest (d less than 10 nm) regularly spaced and shaped spherically, the larger (up to 65 nm) being cylinders or slits. Apparently, at a nanoscale level diatomaceous silica is quite homologous among species, in agreement with the chemical principles of silica polymerization under the conditions of pH and precursor concentrations inside the silicon deposition vesicle. The final frustule "macro"-morphology is of course species-specific, being determined genetically. Synthetically-derived MCM-type silicas have a similarly organized pore distribution in an amorphous silica matrix as we found in all diatom species studied. We therefore suggest that organic molecules of a kind used as structure-directing agents to produce these artificial silicas play a role in the nucleation of the silica polymerization reaction and the shaping of pore morphology inside the silicon deposition vesicle of diatoms. Structure-directing molecules now await isolation from the SDV, followed by identification and characterisation by molecular techniques. 相似文献
998.
Muscarinic acetylcholine receptors: structure and function 总被引:4,自引:0,他引:4
999.
F. Marsolat D. Tromson N. Tranchant P. Bergonzo F. Moignau L. De Carlan D. Lazaro M. Agelou C. Bassinet C. Huet S. Derreumaux M. Chea G. Boisserie I. Buchheit V. Marchesi 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2012
1000.
Molecular determinants of visual pigment function. 总被引:1,自引:0,他引:1
M L Applebury 《Current opinion in neurobiology》1991,1(2):263-269
Mutagenesis studies and comparisons of natural variants of rhodopsin and related visual pigments have led to new insights concerning photoreceptor function. The studies identify domains important for receptor folding, the residues that set the wavelength of absorption for the ligand 11-cis retinal, and residues, that when mutated, trigger the cell death of photoreceptors. 相似文献