全文获取类型
收费全文 | 148321篇 |
免费 | 9224篇 |
国内免费 | 994篇 |
出版年
2023年 | 1061篇 |
2022年 | 1345篇 |
2021年 | 2601篇 |
2020年 | 2129篇 |
2019年 | 2324篇 |
2018年 | 4387篇 |
2017年 | 3866篇 |
2016年 | 5216篇 |
2015年 | 6869篇 |
2014年 | 7175篇 |
2013年 | 9406篇 |
2012年 | 10964篇 |
2011年 | 9847篇 |
2010年 | 6207篇 |
2009年 | 4819篇 |
2008年 | 7350篇 |
2007年 | 6903篇 |
2006年 | 6610篇 |
2005年 | 5645篇 |
2004年 | 5545篇 |
2003年 | 4958篇 |
2002年 | 4482篇 |
2001年 | 3302篇 |
2000年 | 3199篇 |
1999年 | 2491篇 |
1998年 | 1197篇 |
1997年 | 904篇 |
1996年 | 959篇 |
1995年 | 877篇 |
1994年 | 782篇 |
1993年 | 655篇 |
1992年 | 1448篇 |
1991年 | 1313篇 |
1990年 | 1220篇 |
1989年 | 1278篇 |
1988年 | 1100篇 |
1987年 | 1078篇 |
1986年 | 990篇 |
1985年 | 1090篇 |
1984年 | 931篇 |
1983年 | 783篇 |
1979年 | 854篇 |
1978年 | 676篇 |
1975年 | 754篇 |
1974年 | 809篇 |
1973年 | 783篇 |
1972年 | 698篇 |
1970年 | 665篇 |
1969年 | 720篇 |
1968年 | 681篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The 24 hour urinary free cortisol and cortisone excretion after an oral 100 g glucose load was measured in 60 males (aged 22-56) divided into three groups. G-I consisted of 10 healthy men, G-II of 37 surgical patients and G-III comprised 23 patients with atherosclerotic peripheral vascular disease. The followed subjects responded to the glucose ingestion accordingly to their cortisol excretion. Subjects with an urinary cortisol excretion up to 200 micrograms/24 h responded to the glucose load with an increase of excretion in free cortisol and cortisone. Subjects with the excretion of cortisol above 200 micrograms/24 h responded unambiguously with a decrease in their excretion. We suggest that these changes in both directions can be explained by the available amount of NADPH in the liver. In patients with atherosclerotic peripheral vascular disease, in whom disturbances in lipid and carbohydrate metabolism can be proposed, the response of free corticoids, namely the respond of cortisone, are unequal. 相似文献
992.
The binding of Bacteroides intermedius VPI 8944 to human fibrinogen has been characterized. The binding is time dependent, at least partially reversible, saturable, and specific. On an average, a maximum of 3,500 fibrinogen molecules bind per bacterial cell, with a dissociation constant of 1.7 X 10(-11) M. These bacteria also exhibit a fibrinogenolytic activity which can be partially inhibited by protease inhibitors. Bacteria release fibrinogenolytic activity into the surrounding medium without loss of binding activity, but more pronounced fibrinogen breakdown occurs when 125I-labeled fibrinogen is associated with the bacteria, suggesting that fibrinogen is degraded at the cell surface. Fibrinogen binding by B. intermedius might represent a mechanism of bacterial tissue adherence. 相似文献
993.
994.
Methylation of type II and type I collagen genes in differentiated and dedifferentiated chondrocytes 总被引:2,自引:0,他引:2
The methyl-sensitive restriction endonucleases HpaII and HhaI as well as the methyl-insensitive enzyme MspI were used to examine the methylation status of the pro-alpha 1(II) collagen gene of cartilage. Five different cell types with varying abilities to express type II collagen were studied. Chick embryo chondrocytes express type II collagen, while 5-bromodeoxyuridine-treated chondrocytes, retinoic acid-treated chondrocytes, chick embryo fibroblasts, and erythrocytes do not synthesize type II collagen. Both cDNA and genomic probes for the pro-alpha 1(II) collagen gene were used, covering the complete 3' end of the gene and its flanking sequences. The pro-alpha 1(II) collagen DNA was undermethylated in chondrocytes, compared to either fibroblasts or erythrocytes. However, the methylation of the 5-bromodeoxyuridine-treated and retinoic acid-treated chondrocytes was identical to that of control chondrocytes. The methylation pattern of two regions of the gene of the pro-alpha 2(I) collagen chain was identical in all cell types tested, whether or not the gene was expressed. Our results indicate that genes for these collagen chains differ in their methylation pattern. The type II collagen gene shows reduced methylation in expressing cartilage, but does not acquire an increase in methylation in "dedifferentiated" chondrocytes. The changes in DNA methylation that occur during cell differentiation do not appear to be sufficient to explain gene activation and deactivation. 相似文献
995.
The changes of H-D exchange rates upon protein-protein interactions are generally interpreted as a result of the changes of the dynamic properties of the proteins. The effect of trypsin binding on the H-D exchange kinetics of some trypsin inhibitor amide H's was reported (Simon et al., 1984). In this paper the electrostatic potential originating from the trypsin molecule is calculated at the positions of the studied amide H's in the trypsin-trypsin inhibitor complex. We conclude that the observed decrease of the exchange rates is mainly due to the electrostatic field of the trypsin molecule. 相似文献
996.
Summary Monoclonal antibodies able to recognize single antigenic determinants are a powerful tool for the study of immunological heterogeneity of antigens. In this paper we have used a monoclonal antibody against the -subunit of pig brain tubulin (TU-01) to investigate the immunoreactivity of tubulins from mammals, avians, amphibia, echinodermata, plathelmints, slime moulds and protozoa. Immunoreactivity was detected using immunoblotting and indirect immunofluorescence of isolated cells. Our results show that the antigenic determinant recognized by the TU-01 antibody is present in all metazoan tubulin tested and among the eukaryotic microorganisms only in the flagellateTrichomonas vaginalis. Indirect immunofluorescence also reveals that not allTrichomonas microtubules are stained by TU-01 antibody indicating the presence of different tubulins within a single cell. This results are consistent with the multitubulin hypothesis (Fulton andSimpson 1976). 相似文献
997.
Summary Using the monotone dependence function (mdf) together with correlation coefficient it was found that the Ma-DNA content as well as total protein content are regularly, linearly, positively and strongly dependent in sister cells (proter-opisthe) ofChilodonella steini. Additionally it was shown that proter-opisthe ordering is irrelevant to Ma-DNA and protein contents.Analysis of sister cell generation times (TG) confirmed the existence of regular, linear, positive and strong codependence.The relations between Ma-DNA and total protein contents, between protein content and TG, and between Ma-DNA content and TG were also described. There is a weak, linear dependence between Ma-DNA and total protein contents. Relations of TG and Ma-DNA content or TG and total protein content are non-linear and not even monotone. Low and high levels of DNA or proteins are connected with long generation times. 相似文献
998.
Eight plant lectins were used to investigate membrane alterations in lymphocytes from patients with chronic lymphocytic leukemia (CLL). By rosetting with lectins attached to latex particles, the cell percentages with the abundance of each lectin receptor were compared in B normal and leukemic lymphocytes. Comparing these data with the number of lectin molecules bound to each cell and the affinity, which are values calculated with 125I-labeled lectins, it was possible to deduce differences in the composition of glycoproteins in B normal and B-CLL lymphocytes membrane. Compared to B normal, B-CLL lymphocytes had fewer receptors for WGA and more for Lens culinaris, SBA and Tetragonolobus purpureus lectins. Receptors for Concanavalin A, Pisum sativum, PHA and Tetragonolobus purpureus showed a higher affinity with B normal lymphocytes, while the other lectins assayed showed more affinity with B-CLL lymphocytes. So, it is possible to establish a comparative analysis about the plasma membrane glycoproteins in the B normal and CLL lymphocytes by lectin binding studies. 相似文献
999.
The enzymatic activities of two "key" enzymes of the glycolytic pathway, pyruvate kinase and lactic dehydrogenase, were studied in seven areas of the brain in male adult rats in states of pharmacologically induced hyper and hypothyroidism. The brain areas were: anterior cortex, adenohypophysis, hypothalamus, amygdaline nucleus, septum, hippocampus and cerebellum. In T3 treated animals, pyruvate kinase activity showed significant increase in all the areas studied while lactic dehydrogenase activity decreased. In propyl-thiouracil treated animals these enzyme activities showed no significant variations from those in animals of the control group. 相似文献
1000.
J M Fernández M F Rubio-Arroyo M Soriano-García R A Toscano M C Pérez-César 《Steroids》1985,45(2):151-157
The synthesis and molecular structure of prolame, N-(3-hydroxy-1,3,5(10)-estratrien-17 beta-yl)-3-hydroxypropylamine, is described. It was characterized by ir, nmr, mass spectrometry and chemical analysis. The crystal structure of this compound was determined by single-crystal x-ray diffraction. Prolame belongs to space group P212121. Cell dimensions are: a = 8.356(2), b = 13.343(4) and c = 16.119(4) A. Z = 4; R = 4.1%. 相似文献