全文获取类型
收费全文 | 8234篇 |
免费 | 858篇 |
国内免费 | 3篇 |
出版年
2023年 | 48篇 |
2022年 | 74篇 |
2021年 | 151篇 |
2020年 | 136篇 |
2019年 | 182篇 |
2018年 | 185篇 |
2017年 | 206篇 |
2016年 | 321篇 |
2015年 | 474篇 |
2014年 | 470篇 |
2013年 | 581篇 |
2012年 | 636篇 |
2011年 | 575篇 |
2010年 | 461篇 |
2009年 | 383篇 |
2008年 | 462篇 |
2007年 | 421篇 |
2006年 | 365篇 |
2005年 | 406篇 |
2004年 | 377篇 |
2003年 | 370篇 |
2002年 | 327篇 |
2001年 | 79篇 |
2000年 | 56篇 |
1999年 | 97篇 |
1998年 | 73篇 |
1997年 | 62篇 |
1996年 | 67篇 |
1995年 | 57篇 |
1994年 | 51篇 |
1993年 | 50篇 |
1992年 | 59篇 |
1991年 | 44篇 |
1990年 | 47篇 |
1989年 | 50篇 |
1988年 | 37篇 |
1987年 | 42篇 |
1986年 | 40篇 |
1985年 | 24篇 |
1984年 | 47篇 |
1983年 | 35篇 |
1982年 | 41篇 |
1981年 | 32篇 |
1980年 | 37篇 |
1979年 | 29篇 |
1978年 | 28篇 |
1977年 | 22篇 |
1976年 | 27篇 |
1975年 | 27篇 |
1974年 | 23篇 |
排序方式: 共有9095条查询结果,搜索用时 15 毫秒
131.
Nitrate reductase activity in the leaves of young plants of cucumber.Cucumis sativus L. cv. Bílská, as determined bothin vitro andin vivo and expressed in terms of fresh weight, gradually changes in dependence on the ontogenetic development of the plants, reaching
its maximum before full expansion of the leaves. 相似文献
132.
Octahedral shaped crystals of about 1 mm were grown from catalase of Micrococcus luteus. The space group was determined as P422121 with . In contrast to mammalian catalase, the bacterial catalase contains only one subunit per asymmetric unit. This proves that the four subunits of bacterial catalase are identical. 相似文献
133.
Summary The mitochondrial ATPase from a PHO 1 mutant (OLI 2, PHO 1, OLI 4 region on mit DNA of S. cerevisiae) was further examined. A new purification method using Lysolecithin instead of Triton allowed us to solubilize and separate a heterogeneous ATPase population from PHO 1-mitochondria: the major abnormal fraction had extremely low oligomycin-sensitivity (but normal specific immunological reactivity), while a minor normal fraction (representing about 20% of the initial mitochondrial ATPase activity) had high sensitivity and affinity for oligomycin.Moderate urea treatment of PHO 1-mitochondria leads to partial loss of ATPase activity and a concomitant increase of oligomycin-sensitivity, suggesting that a heterogeneous ATPase population exists in situ in the mitochondrial membrane: part of the major abnormal ATPase fraction is selectively inactivated by urea, producing a concomitant enrichment in the initially minor normal ATPase fraction.If the minor normal ATPase fraction is the only one capable of in vivo ATP synthesis, the deficient but oligomycin-sensitive cell growth and oxidative phosphorylation in vitro are readily explained.Further structural studies are under way to ascertain whether the minor normal ATPase fraction is strictly identical to the wild type, in which case PHO 1 is a regulatory gene, or not, in which case PHO 1 is a structural gene. 相似文献
134.
The nature and distribution of hemotypes constituted by electrophoretic phenotypes in six loci, in a group of 183 Camargue horses, have been compared with those of five breeds of horses and ponies. The genetic similarities have been observed mainly with New Forest and Haflinger ponies, less with Barbs and Thoroughbreds, and the least with Arab horses. 相似文献
135.
Axel Kahn Joelle Marie Juan Luis Vives-Corrons Pierre Maigret Albert Najman 《Human genetics》1981,57(2):172-175
Summary Anomalies of the mutant pyruvate kinase variants and clinical symptoms have been compared in 22 unrelated patients with congenital red cell pyruvate kinase deficiency. This study suggests that some characteristics of the mutant enzymes could play a role in the intensity of haemolysis, namely residual activity, affinity for the substrate phosphoenolpyruvate and for the allosteric activator fructose 1,6 diphosphate and inhibition by ATP. 相似文献
136.
Marie M. Roberson Howard Ceri Paula J. Shadle Samuel H. Barondes 《Journal of cellular biochemistry》1981,15(4):395-402
Extracts of young rat lung contain a heparin-inhibitable lectin that closely resembles one recently purified from chicken liver. Both lectins interact with heparin and N-acetyl-D-galactosamine, and were purified by gel filtration on Sepharose CL-2B followed by affinity chromatography on heparin-Sepharose. They both behave as high molecular weight aggregates that can be dissociated into two peptides with apparent molecular weights of 13,000 and 16,000 by gel electrophoresis in SDS. Samples of purified lectin contained up to 20% DNA by weight, and the degree of lectin aggregation and hemagglutination activity was greatly reduced by treatment with micrococcal nuclease without inhibiting heparin-binding activity. Association of lectin with DNA is an artifact of homogenization in high salt, since only 2% of the lectin is found associated with a purified nuclear fraction. 相似文献
137.
Prof. Dr. L. Bjersing S. Cajander J. -E. Damber P. O. Janson B. Källfelt 《Cell and tissue research》1981,216(3):471-479
Summary In the present investigation the ultrastructure of isolated rabbit ovaries, perfused with different media for various time periods, was studied. The steroid hormone production by the perfused ovary was also determined. Perfusion with Medium 199 results in prominent interstitial ovarian oedema which increases with perfusion time. Even after the addition of 6–10 % Dextran T40, oedema appears in the interstitial tissue of the ovary. Perfusion solutions with osmotically active colloid particles of large molecular size (Dextran T70; average molecular weight 70,000 and bovine serum albumin), cause less distortion in the ovarian structure, and ultrastructurally the ovarian tissues appear essentially the same as in the control ovaries.The results indicate that the perfused rabbit ovary, under strictly controlled conditions, can be used as an experimental model for studies of various aspects of ovarian function, including follicular rupture. 相似文献
138.
Summary Two unrelated patients were found to be mosaic for an extra chromosome 9 (46,XX/47,XX,+9). The first patient showed a prominent nose, deep set eyes, carp shaped mouth and complex congenital cardiac anomalies. She died of congestive cardiac failure at the age of 10 days. The second patient, was a 7 1/2 year old female who had persistent alacrimia and mental retardation. 相似文献
139.
Involvement of IS1 in the dissociation of the r-determinant and RTF components of the plasmid R100.1
Summary Detailed mapping localized the PHO 1 mutation between the OLI 2 and OLI 4 loci on mitochondrial DNA of Saccharomyces cerevisiae.In its mitochondrially integrated form, the PHO 1-ATPase3 was difficult to identify either immunologically or by specific inhibitors like oligomycin and DCCD. Solubilization by Triton X-100 allowed unambiguuous identification of this enzyme as an authentic mitochondrial ATPase. However, Triton extraction produced a 2 to 3 fold enhancement of the PHO 1-ATPase activity which also became drastically cold-sensitive. The wild type ATPase was neither activated nor made cold-labile by solubilization, and retained full sensitivity to oligomycin and DCCD.Sucrose gradient analysis of the Triton-extracted ATPase from wild type, PHO 1 mutant and rho
-
strains showed a density difference between the solubilized PHO 1-and wild type ATPase, and similarity between solubilized PHO 1-and rho
- ATPase (F1).Whole cells of the PHO 1 mutant present considerably increased respiration rates.Comparison of oligomycin-sensitivity in whole cells, coupled isolated mitochondria and membrane-bound ATPase indicates a contrast between oligomycin-resistance of the ATPase and oligomycin-sensitivity of in vivo or in vitro coupling systems, which might characterize the products of this region of mitochondrial DNA. 相似文献
140.
Testicular blood flow and testosterone concentration in spermatic venous blood of anaesthetized rats
Testicular blood flow was measured by a radioactive microsphere technique. A significant correlation, rs equal to 0.82, was found between testicular blood flow and testosterone outflow in the spermatic venous blood, indicating that factors which affect the testicular circulation may influence testicular endocrine function. 相似文献