全文获取类型
收费全文 | 60683篇 |
免费 | 3806篇 |
国内免费 | 9篇 |
出版年
2023年 | 378篇 |
2022年 | 351篇 |
2021年 | 842篇 |
2020年 | 741篇 |
2019年 | 815篇 |
2018年 | 1746篇 |
2017年 | 1509篇 |
2016年 | 2111篇 |
2015年 | 2891篇 |
2014年 | 2989篇 |
2013年 | 3984篇 |
2012年 | 4556篇 |
2011年 | 4190篇 |
2010年 | 2664篇 |
2009年 | 2038篇 |
2008年 | 3249篇 |
2007年 | 3156篇 |
2006年 | 3043篇 |
2005年 | 2613篇 |
2004年 | 2534篇 |
2003年 | 2286篇 |
2002年 | 2127篇 |
2001年 | 1375篇 |
2000年 | 1285篇 |
1999年 | 1027篇 |
1998年 | 468篇 |
1997年 | 331篇 |
1996年 | 351篇 |
1995年 | 342篇 |
1994年 | 252篇 |
1993年 | 234篇 |
1992年 | 612篇 |
1991年 | 520篇 |
1990年 | 492篇 |
1989年 | 461篇 |
1988年 | 413篇 |
1987年 | 407篇 |
1986年 | 365篇 |
1985年 | 398篇 |
1984年 | 313篇 |
1983年 | 260篇 |
1982年 | 224篇 |
1981年 | 208篇 |
1979年 | 324篇 |
1978年 | 228篇 |
1974年 | 242篇 |
1973年 | 227篇 |
1972年 | 204篇 |
1971年 | 207篇 |
1970年 | 202篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
42.
I Monta?és A Badía M A Réngel J M López-Novoa 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1992,199(3):321-326
Renal metabolism has been studied in eight dogs before and 48 hr after a 60-min period of renal ischemia induced by clamping the left renal artery with the simultaneous removal of the right kidney, and in 12 sham-operated animals. The study involved the measurement of renal uptake and production of lactate, glutamine, glutamate, alanine, ammonium, and oxygen, and the measurement of the tissue concentrations of ATP, glutamine, lactate, alpha-ketoglutarate, aspartate, and alanine in the renal cortex. Two days after a temporary renal ischemia, the remaining kidney showed a 22% decrease in glomerular filtration rate (GFR) and a 25% decrease in renal plasma flow. Fractional sodium and potassium excretions were similar to those of control dogs. Renal production or extraction of glutamine, glutamate, alanine, ammonium, and oxygen (all expressed by 100 ml of GFR) was not significantly different in basal conditions or 2 days after ischemia, but lactate extraction was reduced in postischemic kidneys (-101 +/- 29 vs -204 +/- 38 mumol/100 ml GFR in control dogs). The cortical concentrations of glutamine and glutamate were lower in postischemic than in control kidneys. No differences were found in cortical concentration of alpha-ketoglutarate, aspartate, lactate, pyruvate, or ATP, but total nucleotides and inorganic phosphate were decreased in postischemic kidneys. It is concluded that in the recovery phase of the ischemia, a decreased lactate uptake is the main metabolic change, and total ATP production is adapted to the decrease of GFR and sodium reabsorption. 相似文献
43.
It is shown that the light microscopic permanent detectable phenoloxidase activity, using dihydroxyphenylalanine as substrate, of the small intestine of white rats is localized in the most cases in eosinophilic granulocytes. The enzyme has been found as well in the cytoplasma as in the granules. The enzyme proof triggered in the granules the so called reverse effect. The results allow to conclude new aspects for the cell mediated immunological defense reaction. 相似文献
44.
45.
Cortinarius sarcoflammeus is proposed as a new species belonging to subgenus Dermocybe, on the basis of its morphological, chemical and ecological characters. The strong red-orange colour of the context and stipe
base, large spores, sphagnicolous habitat and high dermorubin content are characteristic for the new species. Holotypes of
C. huronensis and C. huronensis var. olivaceus have been examined for comparison, and their differences discussed. Photographs and line drawings of C. sarcoflammeus are added.
Received February 13, 2001 Accepted March 23, 2001 相似文献
46.
A new class of Phycomyces behavioral mutants with enhanced tropic responses has been analyzed genetically to determine the number of genes involved and the nature of their expression. These hypertropic mutants carry pleiotropic nuclear mutations. Besides their effects on sensory behavior, they also affect morphology and meiotic processes. Behavioral analyses of heterokaryons containing hypertropic and wild-type nuclei in varying proportions show that the hypertropic mutations in strains L82, L84, L86, and L88 are strongly dominant. Conversely, the hypertropic mutations carried by the strains L83, L85, and L87 are strongly recessive. We performed recombination analyses between hypertropic mutants and mutants with diminished phototropism, affected in the seven genes madA to madG. We found no evidence of linkage between the hypertropic mutations and any of these mad mutations. From crosses, we isolated double mutants carrying hypertropic mutations together with madC (night blind) and madG (stiff) mutations. The behavioral phenotypes of the double mutants are intermediate between those of the parentals. Complementation analyses show that the three recessive hypertropic mutations affect the same gene, which we call madH. The expression of the recessive hypertropic allele becomes dominant in heterokaryons carrying madC and madH nuclei; the madC gene has been implicated separately with the photoreceptor at the input to the sensory pathway, while the madH gene is associated with the growth control output. This result suggests the physical interaction of both gene products, madH and madC, in a molecular complex for the photosensory transduction chain. 相似文献
47.
Six peripheral blood lymphoid fractions (total lymphocytes, non-T, T, Tar (autologous rosette-forming T cells/precursor), T mu (helper), and T gamma (suppressor) lymphocytes) isolated through rosetting procedures were examined for the presence of ferritin by a direct immunofluorescence technique. Although ferritin was present in all lymphoid fractions studied, a significantly higher proportion of ferritin-containing cells were detected in the T-cell fraction than in the non-T-cell fraction, (mean +/- SD = 7.9 +/- 1.6% and 5.0 +/- 1.2%, respectively). T mu- and T gamma-cell fractions showed a twofold increase in the number of ferritin-positive cells (14.1 +/- 1.4% and 15.4 +/- 2.6%, respectively), as compared with Tar (7.0 +/- 0.9%)-and total lymphocyte (6.9 +/- 1.3%)-cell fractions. These results indicate that ferritin is preferentially distributed in T mu and T gamma lymphocytes and may constitute the basis for explaining some of the roles exercised by these cells in the control of other biological systems. 相似文献
48.
49.
50.