全文获取类型
收费全文 | 562943篇 |
免费 | 55254篇 |
国内免费 | 243篇 |
出版年
2016年 | 6247篇 |
2015年 | 7721篇 |
2014年 | 9402篇 |
2013年 | 13992篇 |
2012年 | 15315篇 |
2011年 | 16124篇 |
2010年 | 11050篇 |
2009年 | 10137篇 |
2008年 | 14533篇 |
2007年 | 15320篇 |
2006年 | 14393篇 |
2005年 | 13746篇 |
2004年 | 13863篇 |
2003年 | 13546篇 |
2002年 | 13392篇 |
2001年 | 23673篇 |
2000年 | 23999篇 |
1999年 | 18818篇 |
1998年 | 6592篇 |
1997年 | 6922篇 |
1996年 | 6470篇 |
1995年 | 6065篇 |
1994年 | 5907篇 |
1993年 | 6032篇 |
1992年 | 16268篇 |
1991年 | 16176篇 |
1990年 | 16023篇 |
1989年 | 15810篇 |
1988年 | 14860篇 |
1987年 | 14000篇 |
1986年 | 12996篇 |
1985年 | 13488篇 |
1984年 | 11138篇 |
1983年 | 9586篇 |
1982年 | 7159篇 |
1981年 | 6405篇 |
1980年 | 6070篇 |
1979年 | 10682篇 |
1978年 | 8338篇 |
1977年 | 7756篇 |
1976年 | 7314篇 |
1975年 | 8145篇 |
1974年 | 9020篇 |
1973年 | 8851篇 |
1972年 | 8244篇 |
1971年 | 7499篇 |
1970年 | 6537篇 |
1969年 | 6446篇 |
1968年 | 6019篇 |
1967年 | 5259篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
The breeding cycles of two species of sandy beach whelk (Bulliadigitalis and B. pura) are presented and compared with a thirdspecies (B. rhodostoma). In all three species, egg maturationand copulation occur in spring while summer marks the depositionand spawning of egg capsules. B. digitalis and B. pura migrateoffshore to lay their eggs, the juveniles of both species restrictingthemselves to beyond the breaker zone. Newly hatched snailsof B. rhodostoma appear in the intertidal towards late summer.The discovery of a penis-like structure on females of B. rhodostomais investigated. The pseudopenis was also found on B. pura butnever on B. digitalis. The possibility of a sex-change was eliminatedon the histological investigation of the gonads of a range ofsnails and the examination of sex-ratios over a period of fivemonths. General trends in reproductive behaviour are also discussed. (Received 18 March 1984; 相似文献
103.
G S Aulakh E B Stephens D L Rose J G Tully M F Barile 《Journal of bacteriology》1983,153(3):1338-1341
3H-labeled Acholeplasma DNA probes were generated in vitro by the nick-translation method and used to determine the nucleotide sequence homology among the type strains of the eight currently recognized species of Acholeplasma. Very little nucleotide sequence homology (less than or equal to 18%) was found among the eight species, with heteroduplexes showing at least 12% or more mismatching as determined by thermal elution midpoints. The small amount of nucleotide sequence homology among the eight species indicates that these species are quite distinct and are not closely related to each other genomically. 相似文献
104.
The complete primary structure of the functional site of erythrocyte protein 4.1 involved in spectrin-actin associations has been determined. The sequence of this domain, which contains 67 amino acids and has a molecular mass of 8045 daltons, has been obtained by NH2-terminal sequence analysis of an 8-kDa chymotryptic peptide, three endoproteinase lysine C-cleaved peptides and two peptides obtained by Staphylococcus aureus protease V8 cleavage. All peptides including the 8-kDa domain peptide were purified by reverse-phase high performance liquid chromatography. Antibodies against two different synthetic peptides of the 8-kDa domain are able to inhibit the association between protein 4.1, spectrin, and F-actin, corroborating that the 8-kDa domain is responsible for the formation of a ternary complex. A computer search of the 8-kDa sequence with the National Biomedical Research Foundation database did not detect any significant homologies to known sequences. Protein 4.1 is not related to any known proteins and may represent a new protein superfamily. 相似文献
105.
Monosomy 21: a new case confirmed by in situ hybridization 总被引:4,自引:0,他引:4
M. C. Pellissier N. Philip M. A. Voelckel-Baeteman M. G. Mattei J. F. Mattei 《Human genetics》1987,75(1):95-96
Summary A new case of total monosomy 21 in a newborn is described. The diagnosis was first made using the cytogenetic data; it was then confirmed by the dosage of copper-superoxide dismutase (SOD-1) which showed a 50% decrease. In situ hybridization with a probe previously assigned to chromosome 21 was used to rule out the possibility of a partial monosomy with an unbalanced reciprocal translocation. 相似文献
106.
A series of measurements of blood pressure in normotensive and hypertensive subjects showed that measurements made with a sphygmomanometer with the arm dependent by the side were consistently higher than those made with the arm horizontal at heart level. The mean difference in a group of 90 hypertensive outpatients was 11/12 mm Hg. Failure to appreciate the importance of arm position may lead to erroneous measurements of blood pressure. This has important implications for clinical practice and research. 相似文献
107.
108.
A. V. Nikolayev Yu. V. Kirichek O. I. Ostrovskaya I. I. Maletina K. I. Petko L. M. Yagupol’skii 《Neurophysiology》1999,31(3):191-193
With the use of a patch-clamp technique in the whole-cell configuration, we studied the effects of pinacidil and its fluorine
derivatives on A-type potassium current (I
A) through the membrane of pyramidal neurons of the rat hippocampus. Hydrogen peroxide (10 mM) exerted no influence on the
rate of inactivation ofI
A; therefore, this current is probably mediated by Shal Kv4.2 potassium channels. Pinacidil demonstrated the properties of
a weakI
A blocker: in the 500 μM concentration it blocked about 45% of the current, while 50 μM of pinacidil fluorine derivatives were
capable of blocking up to 30% ofI
A. The effects of pinacidil and its derivatives showed no dependence on the stimulating potential. A similar pattern of the
effects of pinacidil fluorine derivatives, which are an order of magnitude stronger than those of pinacidil itself, allows
us to suppose that the imine nitrogen of the tested compounds is significantly more involved in the molecular interaction
with the site of an A-type potassium channel than the pyridine nitrogen. 相似文献
109.
110.