全文获取类型
收费全文 | 883555篇 |
免费 | 90762篇 |
国内免费 | 587篇 |
出版年
2018年 | 8188篇 |
2017年 | 8070篇 |
2016年 | 12123篇 |
2015年 | 17304篇 |
2014年 | 19410篇 |
2013年 | 25946篇 |
2012年 | 27607篇 |
2011年 | 26082篇 |
2010年 | 18131篇 |
2009年 | 16954篇 |
2008年 | 22210篇 |
2007年 | 22640篇 |
2006年 | 21771篇 |
2005年 | 26221篇 |
2004年 | 24694篇 |
2003年 | 22623篇 |
2002年 | 20049篇 |
2001年 | 40339篇 |
2000年 | 40220篇 |
1999年 | 32381篇 |
1998年 | 10598篇 |
1997年 | 11036篇 |
1996年 | 10448篇 |
1995年 | 9596篇 |
1994年 | 9651篇 |
1993年 | 9539篇 |
1992年 | 26988篇 |
1991年 | 26432篇 |
1990年 | 25888篇 |
1989年 | 25702篇 |
1988年 | 23860篇 |
1987年 | 22464篇 |
1986年 | 20634篇 |
1985年 | 20921篇 |
1984年 | 16564篇 |
1983年 | 14459篇 |
1982年 | 10562篇 |
1981年 | 9469篇 |
1980年 | 8996篇 |
1979年 | 15840篇 |
1978年 | 12260篇 |
1977年 | 11093篇 |
1976年 | 10422篇 |
1975年 | 11751篇 |
1974年 | 12576篇 |
1973年 | 12434篇 |
1972年 | 11196篇 |
1971年 | 10214篇 |
1970年 | 9091篇 |
1969年 | 8509篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
I. T. Rass 《Biochemistry. Biokhimii?a》2010,75(3):353-366
Glucocorticoid hormones directly or indirectly control virtually all metabolic and physiological processes. Glucocorticoids
are also shown to act on a multitude of genes, enzyme systems, and proinflammatory factors, but for these hormones there is
no representative index of action on metabolism similar to glucose content in blood for insulin. The absence of such an index
prevents the assessment of tissue provision with these hormones under various conditions and seems to be an essential cause
of complications associated with the clinical use of glucocorticoid preparations. Considering specific features of tyrosine
metabolism and data obtained experimentally and on a clinical model (adrenalectomy in rats and substitution therapy in endocrine
disease), blood content of this amino acid seems promising as such an index. Based on comparing results of glucocorticoid
treatment in patients with systemic lupus erythematosus with changes in their blood tyrosine contents, the pharmacological
effect of glucocorticoid preparations is suggested to be mainly due to compensating a relative shortage of these hormones. 相似文献
992.
P T M?nnist? 《Medical biology》1980,58(6):310-318
The subcellular distribution of the TRH-like immunoreactivity in the rat hypothalamus and brain was studied. In differential centrifugation, the 900 g for 10 min supernatant (S1) of the hypothalamus or brain contained 61--79% of the total TRH. At 11,000 g for 20 min, 51--73% of the TRH in S1 was sedimented. When the hypothalamic S1 was fractioned under non-equilibrium conditions at 25 degrees C, two populations of TRH-containing particles were observed in several types of continuous linear density gradients. Metrizamide and sucrose gradients affected TRH-assay. TRH-particles were very light in Percol-gradients. Isotonic dextran 40,000-sucrose gradients gave the most reproducible results. In these gradients, the large TRH-particles (35%) equilibrated at 1.055--1.060 kg/l and the small ones (23%) at 1.041--1.047 kg/l. Working at 4 degrees C decreased the amount of large TRH-particles. The apparently larger particles contained cytoplasmic and mitochondrial enzymes and were sensitive to hypoosmotic shock like synaptosomes. Electron micrographs confirmed that these particles were synaptosomes. The true nature of the small particles remained unclear but morphologically a part of them were also synaptosomes. Treatment of the animals with reserpine (10 mg/kg i.p., 24 h), with 6-hydroxydopamine (100 microgram/rat i.c.v.) or with 5,7-dihydroxytryptamine (200 microgram/rat i.c.v.) did not affect significantly TRH-recovery or distribution in the hypothalamus. 相似文献
993.
C D Wolleben R K McPherson J Rulfs G L Johnson T B Miller 《Biochimica et biophysica acta》1987,928(1):98-106
The phosphorylation of glycogen synthase has been studied in freshly isolated adult rat cardiomyocytes. Six peaks of 32P-labeled tryptic peptides are recovered via C-18 high performance liquid chromatography (HPLC) when synthase is immunoprecipitated from 32P-labeled cardiomyocytes and digested with trypsin. When epinephrine treated cells are used as a source of enzyme, the same HPLC profile is obtained with a dramatic enhancement of 32P recovered in two of the HPLC peaks. In vitro phosphorylation of rat heart synthase by cAMP-dependent protein kinase stimulates the conversion of synthase from the I to the D form and results in the recovery of the same tryptic peptides from the C-18 as is the case for synthase derived from cardiomyocytes. Treatment of cAMP-dependent kinase phosphorylated synthase with protein phosphatase-1 leads to a reactivation of the enzyme and a dephosphorylation of the same tryptic peptides that are selectively phosphorylated in epinephrine treated cardiomyocytes. These results are discussed in relation to hormonal control of glycogen metabolism in cardiac tissue. 相似文献
994.
P. Webb A. D. Chanana E. P. Cronkite J. A. Laissue D. D. Joel 《Cell proliferation》1980,13(3):227-237
Germ-free (GF) and conventional (CV) C3H mice received a single injection of 1 μCi [3H]thymidine and 3 μCi [125I]iododeoxyuridine to provide simultaneous labeling of DNA with the two precursors. Thymus, spleen, mesenteric lymph nodes, bone marrow (femora), small intestine, colon and skin were examined for total organ activity and rate of DNA renewal 1–8 days after injection. Precursor incorporation, assayed on day 1, was lower in the thymus, mesenteric lymph nodes and femora (and, to a lesser extent, in the spleen and colon) of GF mice as compared to CV animals. The opposite was observed in the small intestine and skin, i.e. total organ activity was higher in GF animals. Differences in precursor incorporation were partly due to differences in organ weights between the two groups of mice. In comparison to CV animals, DNA renewal rates were diminished in the mesenteric lymph nodes, bone marrow, colon (following a 3-day plateau) and spleen of GF mice. Little, if any, difference was observed between the two groups with respect to the rate of DNA turnover in the thymus and skin. Radioactivity of the small intestine remained constant for 2 days. Thereafter intestinal activity in GF mice declined at an initial slow rate between days 2 and 5 followed by a rapid decrease between days 5 and 8. In CV mice the first phase of activity loss was short with the rapid decline in intestinal activity beginning on day 3. From the slopes of the regression lines, the percentage thymidine reutilization was estimated. Reutilization varied from 0 to 63% in the various organs examined, with the greatest difference between GF and CV mice occurring in the mesenteric lymph nodes. 相似文献
995.
The present study has shown that on the level of the parasitic system the epidemic process is a biological system, wherein the host population serves as the internal regulator, the mechanism of transmission serves as the external regulator and the parasite population, as the regulated object. The biological regulating mechanisms of the epidemic process have fundamental differences in the groups of infectious with various mechanisms of transmission, and the specific nature of the mechanism of transmission determines the peculiar features of the biological mechanism which governs the self-regulation of the epidemic process. In contrast, on a higher level of the organization of the epidemic process, i. e. on the level of the socio-ecological system, the epidemic process is a biosocial system, wherein the human society serves as the regulator, the parasitic system serves as the regulated object and the mechanism of transmission plays the role of the filter which determines the scope of social factors, most important in the regulation of the epidemic process in a given infection. The spontaneous regulation of the epidemic process is the freed forward channel from the regulator to the regulated object, and the controlled regulation is the feedback channel. 相似文献
996.
997.
Post-translational heterogeneity of the human vitamin D-binding protein (group-specific component) 总被引:4,自引:0,他引:4
D H Coppenhaver N P Sollenne B H Bowman 《Archives of biochemistry and biophysics》1983,226(1):218-223
The vitamin D-binding protein in human serum (the group-specific component) is an alpha 2-globulin which is genetically polymorphic in all populations studied. Previous work (J. Svasti and B. H. Bowman (1978) J. Biol. Chem. 253, 5188-5194, and J. Svasti, A. Kurosky, A. Bennett, and B. H. Bowman (1979) Biochemistry 18, 1611-1617) has shown that the electrophoretic variations of the proteins controlled by two allelic genes, Gc1 and Gc2, are due to at least three amino acid substitutions between Gc1 and Gc2 (Svasti et al. (1979] and to heterogeneity in the Gc1 phenotype arising from carbohydrate dissimilarities. Gc1 migrates electrophoretically as two protein bands, while Gc2 migrates cathodally as a single band. This study demonstrates a post-translational glycosylation difference occurring in a single area of the Gc1 sequence which accounts for the heterogeneity observed previously. The glycosylation site, a threonine residue, appears to be in a sequence which differs between Gc1 and Gc2. The O-glycosidic bond, which is typical of mucins, is rare in plasma proteins. The cyanogen bromide fragment containing the galactosamine-containing carbohydrate in Gc1 was partially sequenced through 20 residues from the amino terminus. No detectable galactosamine could be found in the homologous cyanogen bromide fragment in Gc2. A new purification procedure for the vitamin D-binding protein in human plasma has been developed. Three chromatographic steps provide purified protein. 相似文献
998.
Low-angle laser-light scattering (LALLS) was employed to measure the absolute molecular weight of chicken liver NAD+ kinase (NADK). The weight-average molecular weight (Mw) was found to be 275 000 +/- 15 000. The corresponding value for the second virial coefficient was -1.65 X 10(-3) ml X mol X g2. The value for Mw is in close accord with estimates reported for pigeon liver (270 000) and C. utilis (260 000) NADK. If the active enzyme is a dimer, the weight difference between pigeon/chicken liver and rabbit liver (136 000) NADK would indicate that the latter enzyme is an active monomer unit. 相似文献
999.
Separation of peptides by reverse-phase high-performance liquid chromatography using propyl- and cyanopropylsilyl supports 总被引:2,自引:0,他引:2
The separation of peptides and proteins by reverse-phase high-performance liquid chromatography with cyanopropylsilyl and large-pore propylsilyl supports, together with aqueous trifluoroacetic acid/acetonitrile gradients, was studied. Operating parameters (trifluoroacetic acid concentration, flow rate, and gradient slope) were evaluated using different enzymatic digests of horse cytochrome c and bovine serum albumin. Peptides ranging in size from five amino acids to 68 kDa could be separated on the propylsilyl column in a single chromatographic run. The cyanopropylsilyl column is suitable as a supplement to the use of the large-pore column for medium size (5-20 amino acids) peptides. The chromatographic supports and conditions presented here offer a simple, sensitive, and rapid separation system for a wide size range of peptides and proteins. They extend the versatility of separation methodology for these molecules. 相似文献
1000.
Rare syndromes. The Kaufman-McKusick syndrome. A review of the 44 cases reported in the literature 总被引:1,自引:0,他引:1
A Cantani M L Tacconi N Benincori A Picarazzi D Ceccoli S Gaudino 《Annales de génétique》1987,30(2):70-74
The Kaufman-McKusick syndrome (MK 23670) is a rare autosomal recessive disorder characterized by the triad of hydrometrocolpos, postaxial polydactyly, and congenital heart disease. Multiple other anomalies have been ascribed to this syndrome. Hydrometrocolpos, especially if unrecognized, may be a serious, life-threatening condition in the newborn girl. Forty-four cases have been so far reported in the literature. A great phenotypic variability occurs in this syndrome, therefore making it very difficult to identify the disorder at its presentation and classify it correctly. We shall hereafter review current data regarding the prominent clinical features, the diagnosis and treatment of this syndrome. Problems in genetic counseling will be discussed. 相似文献