全文获取类型
收费全文 | 55158篇 |
免费 | 261篇 |
国内免费 | 550篇 |
专业分类
系统科学 | 1228篇 |
丛书文集 | 243篇 |
教育与普及 | 298篇 |
理论与方法论 | 511篇 |
现状及发展 | 31928篇 |
研究方法 | 664篇 |
综合类 | 18907篇 |
自然研究 | 2190篇 |
出版年
2013年 | 807篇 |
2012年 | 551篇 |
2011年 | 2553篇 |
2009年 | 624篇 |
2008年 | 773篇 |
2007年 | 848篇 |
2006年 | 946篇 |
2005年 | 1118篇 |
2004年 | 2280篇 |
2003年 | 1881篇 |
2002年 | 1542篇 |
2001年 | 1315篇 |
2000年 | 875篇 |
1999年 | 953篇 |
1998年 | 649篇 |
1997年 | 771篇 |
1996年 | 534篇 |
1994年 | 683篇 |
1993年 | 690篇 |
1992年 | 856篇 |
1991年 | 749篇 |
1990年 | 851篇 |
1989年 | 657篇 |
1988年 | 638篇 |
1987年 | 658篇 |
1986年 | 742篇 |
1985年 | 855篇 |
1984年 | 750篇 |
1983年 | 692篇 |
1982年 | 790篇 |
1981年 | 832篇 |
1980年 | 913篇 |
1979年 | 1387篇 |
1978年 | 1269篇 |
1977年 | 1230篇 |
1976年 | 1089篇 |
1975年 | 1102篇 |
1974年 | 974篇 |
1973年 | 1193篇 |
1972年 | 1262篇 |
1971年 | 1324篇 |
1970年 | 1376篇 |
1969年 | 1259篇 |
1968年 | 1248篇 |
1967年 | 1074篇 |
1966年 | 905篇 |
1965年 | 726篇 |
1964年 | 504篇 |
1958年 | 593篇 |
1957年 | 508篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
481.
M Debray-Sachs M Dy H Aurengo B Descamps 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1978,286(2):249-252
CBA Mice were immunized by two intraperitoneal injections of 30 X 10(6) DBA/2 or C57BL/6 spleen cells at days--12 and--2. Peritoneal cell population was obtained at day zero by washing the peritoneal cavity of Mice. Adherent cells were then separated using a 2 hrs. incubation in "Falcon" plates followed by washing. This macrophage-rich peritoneal cell population was found nonspecifically cytotoxic against 51Cr labeled tumoral target cells: P815 X DBA/2 mastocytoma cells, EL4 X C57BL/L lymphoma cells and spontaneous lymphoma AKR cells (same H--2k as CBA). This adherent peritoneal cell cytoxicity was demonstrated after 24 hrs. incubation with the target cells. It was found in nonspecific combination as well as when using target cells syngeneic to the donor. These findings suggest that adherent peritoneal cell cytotoxicity could be at least partly due to macrophages and result from factor (s) released by sensitized lymphocytes in vivo in the same way as has been previously demonstrated in vitro. 相似文献
482.
Triiodothyronine injected daily to pregnant rats for the last week of gestation (50 microgram/100 g b.wt) increased the specific activities of 5 acid glycosidases in the fetal forebrain and cerebellum. Cortisone (50 mg/100 g b.wt) administered in the same period had no effect on cerebellum acid hydrolases, but decreased their activity in the forebrain. 相似文献
483.
The glycoprotein CEA (carcinoembryonic antigen) carries carbohydrate groups, which react with the plant lectins from Agaricus bisporus, Arachis hypogaea (peanut), with Tridacnin from invertebrate clams and with the anti-A lectins from snails. Accordingly, it has cryptantigenic structures, which correspond to the T or T-like antigen, the Tridacnin receptor and to the so called A-like antigen. 相似文献
484.
Summary Silver-staining has been used to identify the nucleolus organizer regions (NORs) in the bharal. These show homology with sheep, goat, cattle and aoudad. The association of the NORs on both telomeres of chromosome 3 results in a ring chromosome. 相似文献
485.
Summary The female: male sex ratio in litters born to C57 black mice immunized with male spleen preparations is 21 and males were stillborn. In additionDrosophila busckii males are H-Y antigen positive. It is argued that H-Y is the primary testicular determinant and that this role is evolutionarily ancient. 相似文献
486.
Summary Natural cell-mediated cytotoxicity of normal murine Peyer's patch cells against Ehrlich ascites carcinoma was found in a short-term51Cr release assay. Peyer's patch and lymph node cells showed natural cytotoxicity at approximately the same level.Acknowledgments. This work was supported by grant No. 10.5 from the Polish Academy of Sciences. 相似文献
487.
R. Riehl 《Cellular and molecular life sciences : CMLS》1980,36(8):961-962
Summary The gonopodium of the mosquitofishHeteradria formosa was studied by transmission electron microscopy. In cross-section the gonopodium shows the following structure from the outside inwards: mutilayered epidermis, basal lamina and central supporting tissue, in which vessels and nerves are embedded. At the top of the gonopodium giant collagen fibres are found, which measure up to 150 m in length and 6 m in diameter. These fibres reinforce the gonopodium.This research was supported by the Deutsche Forschungsgemeinschaft. Address for reprints: Forschungsgruppe Dermatologie der Universität Heidelberg, Im Neuenheimer Feld 324, D-6900 Heidelberg. 相似文献
488.
Summary Epithelial-mesenchymal interaction in the differentiation of duodenal epithelium of fetal rats was investigated by recombination experiments in vitro. The proportion of goblet cells in duodenal epithelium was significantly greater on recombination of developing duodenal epithelium with mesenchyme of the glandular stomach than on recombination with that of the duodenum. Mesenchyme of the glandular stomach or forestomach was better than duodenal mesenchyme in supporting morphogenesis of duodenal epithelium. Treatment of tissues with N-methyl-N-nitro-N-nitrosoguanidine (MNNG) did not affect these tissue interactions.This work was supported by grants-in-aid for cancer research from the Ministry of Education, Science and Culture, Japan.Acknowledgment. The authors wish to express their gratitude to Prof. T. Mizuno of the University of Tokyo for valuable suggestions. 相似文献
489.
Summary We analyzed inheritance of 5Es-1 alleles inP. leucopus and found them to be co-dominant and segregating from a single autosomal locus, thereby verifying assumptions of Mendelian inheritance imfield data. We also described an allele that is silent in hemolysate, but is active in liver extract.Acknowledgment. Laboratory analysis was partially supported by a grant-in-aid (No. 0171-02-240-76) to Kaufman from the Research Foundation of State University of New York. 相似文献
490.
Summary Amylase, - and -glucosidase, - and -galactosidase, -fructosidase, trypsin, aminotripeptidase, leucine-aminopeptidase, prolinase, prolidase glycyl-L-leucine dipeptidase and glycylglycine dipeptidase are present in the 3rd instar larvae ofChilo auricilius.Dr Kishan Singh, Indian Institute of Sugarcane Research, Lucknow, is gratefully acknowledged for providing necessary facilities. 相似文献