全文获取类型
收费全文 | 170376篇 |
免费 | 4907篇 |
国内免费 | 820篇 |
出版年
2021年 | 953篇 |
2020年 | 859篇 |
2019年 | 837篇 |
2018年 | 13381篇 |
2017年 | 12011篇 |
2016年 | 9752篇 |
2015年 | 4040篇 |
2014年 | 3847篇 |
2013年 | 5013篇 |
2012年 | 9476篇 |
2011年 | 17062篇 |
2010年 | 14580篇 |
2009年 | 10177篇 |
2008年 | 13191篇 |
2007年 | 14535篇 |
2006年 | 3844篇 |
2005年 | 3547篇 |
2004年 | 3999篇 |
2003年 | 3710篇 |
2002年 | 3256篇 |
2001年 | 2289篇 |
2000年 | 2046篇 |
1999年 | 1488篇 |
1998年 | 646篇 |
1997年 | 481篇 |
1996年 | 526篇 |
1992年 | 933篇 |
1991年 | 873篇 |
1990年 | 826篇 |
1989年 | 903篇 |
1988年 | 750篇 |
1987年 | 768篇 |
1986年 | 690篇 |
1985年 | 756篇 |
1984年 | 632篇 |
1983年 | 569篇 |
1982年 | 460篇 |
1979年 | 671篇 |
1978年 | 489篇 |
1977年 | 491篇 |
1975年 | 594篇 |
1974年 | 626篇 |
1973年 | 596篇 |
1972年 | 795篇 |
1971年 | 768篇 |
1970年 | 543篇 |
1969年 | 614篇 |
1968年 | 574篇 |
1967年 | 479篇 |
1966年 | 467篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
Eva Klozová Jiřina Švachulová J. Smartt E. Hadač Věra Turková Véra Hadačová 《Biologia Plantarum》1983,25(4):266-273
The seed protein patterns of 12Arachis species were compared by polyacrylamide gel electrophoresis (PAGE), similarities between patterns were measured by the Jaccard
index. Results obtained confirm the close relationships established between members of the genus on morphological grounds
and support the more recent classification schemes.A. villosa andA. correntina could well be regarded as distinct species on grounds of protein differences whileA. macedoi andA. villosulicarpa (although members of the same section, Extranervosae) show considerable differentiation of their protein patterns. Surprisingly,
the formA. ×batizogaea showed less similarity in protein pattern to those of its parental species than might have been expected. The principle value
of seed protein pattern data appears to be in distinguishing species within sections. 相似文献
953.
Jana Pospíšilová Jiřina Slavíkovà J. Tupý Ingrid Tiohá T. Gichner 《Biologia Plantarum》1983,25(3):237-240
954.
Electro-optical measurements on aqueous suspension of purple membrane from Halobacterium halobium 总被引:5,自引:5,他引:0 下载免费PDF全文
The permanent dipole moment, polarizability, and the retinal angle of Halobacterium halobium purple membranes were determined at different pH values. All of the parameters have a maximum between pH 5 and 6. There is a reversal in the direction of the permanent dipole moment near pH 5. The value of permanent dipole moment was determined to be 60 D/protein at pH 6.6, and the value obtained for polarizability was 3 X 10(-28) Fm2/membrane fragment. The retinal angle of all-trans retinal was 0.8 degrees smaller than that of the 13-cis conformation. 相似文献
955.
The influence of several operating variables on the productivity and nutritional quality of Candida utilis under carbon-limited growth conditions was studied. Four responses were analyzed: biomass yield (Y), in vitro dry matter digestibility (d), nucleic acid cotents, and protein content (P). Three operating variables were studied: dilution rate, temperature, and carbon-nitrogen ratio in the growth medium. Correlation describing the influence of operating variables on the studied response parameters were developed. From these correlations response surfaces were drawn. A new function, alpha = PdY, is proposed as a more comprehensive criterion for selecting the optimal conditions under the constraint of satisfying multiple objectives. It is demonstrated to be superior to the yield coefficient alone in this respect, since it accounts for factors that are important to the nutritional aspects of the process. 相似文献
956.
957.
958.
The development of the early atrioventricular conduction system in the embryonic heart 总被引:1,自引:0,他引:1
Recent electrophysiological evidence indicates that periodic spontaneous depolarizations occur in the primordial heart of the bird (and presumably mammal) even before the myocardial cells can contract, and these are initiated in the primordial sinoatrial region. As contractions are generated, these then establish a peristaltic wave. From that time on, during ontogenesis, the contractile sequence follows a regular pattern of development. As chambers form they contract sequentially in the direction of blood flow, even though, in the twisted configuration, myocardial continuities suggest the possibility of short-circuiting the electrical conduction pathways from atrium to bulbus. This implies that, even at these early stages, the electrical properties of the myocardium are not isotropic, and that specialized conduction pathways must exist. To the present time, electrophysiological techniques have limited the direct evidence that can be obtained on these delicate electrically specialized pathways. However, microscopical techniques have permitted studies on the morphological development of the tissue and of the cells in the various regions of the myocardium. The present paper traces the development of cell morphology in these regions, including the development of structural nodes and proximal ventricular fibre pathways, and from these observations, the manner in which the electrical conduction pathways are believed to develop is suggested. 相似文献
959.
Emilio Román Galán Jaun A. Galbis Pérez Mariá A. Arévalo Arévalo 《Carbohydrate research》1983,116(2):255-262
The reaction between 2-(benzylamino)-2-deoxy-d-glycero-l-gluco-heptose and 5,5-dimethyl-1,3-cyclohexanedione yields 1-benzyl-4,5,6,7-tetrahydro-6,6-dimethyl-2-(d-galacto-pentitol-1-yl)-indol-4-one (2). Acid-catalyzed, intramolecular dehydration of 2 under kinetically controlled conditions gives 1-benzyl-4,5,6,7-tetrahydro-2-α-d-lyxofuranosyl-6,6-dimethylindol-4-one; the anomeric configuration of this compound is only suggested. When the dehydration reaction is conducted under thermodynamically controlled conditions, it produces a 1:1 mixture of the α- and β-d-lyxopyranosyl compounds. The structures of the new compounds were elucidated by chemical and physical methods. 相似文献
960.
F Vyskocil J Pilar H Zemková P Svoboda V Vítek J Teisinger 《Biochemical and biophysical research communications》1983,116(2):783-790
Bleomycin 2 X 10(-6) and 6 X 10(-6) mol.1(-1) increased the activity of specific (Na+-K+) ATPase of the rat brain microsomes. It also stimulated the electrogenic (Na+-K+) pump in intact skeletal muscle cells. The blocking effect of vanadyl (+4V) on membrane (Na+-K+) ATPase was eliminated completely by the drug, but the action of vanadate (+5V) was counteracted only partially. Electron paramagnetic resonance spectra revealed the formation of a +4V - bleomycin complex which is still able to activate the (Na+-K+) ATPase. 相似文献