全文获取类型
收费全文 | 28952篇 |
免费 | 3688篇 |
国内免费 | 3篇 |
出版年
2021年 | 255篇 |
2019年 | 251篇 |
2018年 | 288篇 |
2017年 | 260篇 |
2016年 | 479篇 |
2015年 | 761篇 |
2014年 | 839篇 |
2013年 | 1074篇 |
2012年 | 1303篇 |
2011年 | 1208篇 |
2010年 | 773篇 |
2009年 | 740篇 |
2008年 | 1101篇 |
2007年 | 1088篇 |
2006年 | 1003篇 |
2005年 | 967篇 |
2004年 | 947篇 |
2003年 | 950篇 |
2002年 | 917篇 |
2001年 | 917篇 |
2000年 | 912篇 |
1999年 | 768篇 |
1998年 | 397篇 |
1997年 | 369篇 |
1996年 | 349篇 |
1995年 | 321篇 |
1994年 | 320篇 |
1993年 | 336篇 |
1992年 | 681篇 |
1991年 | 628篇 |
1990年 | 611篇 |
1989年 | 660篇 |
1988年 | 565篇 |
1987年 | 602篇 |
1986年 | 475篇 |
1985年 | 564篇 |
1984年 | 478篇 |
1983年 | 385篇 |
1982年 | 399篇 |
1981年 | 358篇 |
1980年 | 329篇 |
1979年 | 435篇 |
1978年 | 382篇 |
1977年 | 336篇 |
1976年 | 314篇 |
1975年 | 334篇 |
1974年 | 382篇 |
1973年 | 361篇 |
1972年 | 305篇 |
1971年 | 286篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
J M Phang S J Downing G C Yeh R J Smith J A Williams 《Biochemical and biophysical research communications》1979,87(2):363-370
L-pyrroline-5-carboxylic acid, an intermediate in the interconversions of glutamic acid, ornithine and proline, is a potent stimulator of the hexose-monophosphate pentose pathway in cultured human fibroblasts. These studies suggest that pyrroline-5-carboxylate reductase, which catalyzes the conversion of pyrroline-5-carboxylate to proline coupled with the oxidation of NADPH, provides the NADP for the observed activation of the hexose-monophosphate pentose pathway. 相似文献
102.
103.
104.
M. S. Leaning S. Gallivan E. S. Newlands J. Dent M. Brampton D. B. Smith K. D. Bagshawe 《BMJ (Clinical research ed.)》1992,305(6857):804-807
OBJECTIVE--To design and evaluate a computer advisory system for the treatment of gestational trophoblastic tumour. DESIGN--A comparison of clinicians'' treatment decisions with those of the computer system. Two datasets were used: one to calibrate the system and one to independently evaluate it. SETTING--Department of medical oncology. PATIENTS--Computerised records of 290 patients with low risk gestational trophoblastic tumour for whom the advisory system could predict the adequacy of treatment. The calibration set comprised patients admitted during 1979-86(227) and the test set patients during 1986-89(63). MAIN OUTCOME MEASURES--The system''s accuracy in predicting need to change treatment compared with clinicians'' actions. The mean time faster that the system was in predicting the need to change treatment. RESULTS--On the calibration dataset the system was 94% (164/174) accurate in predicting patients whose treatment was adequate, recommending change when none occurred in only 10 (6%) patients. In patients whose treatment was changed the system recommended change earlier than clinicians in 39/53 cases (74%), with a mean time advantage of 14.9 (SE 2.02) days. On the test dataset the system had an accuracy of 91% (31/34) in predicting treatment adequacy and a false positive rate of 9% (3/34). The system recommended change earlier than clinicians in 22/29 cases (76%), with a mean time advantage of 12.5 (2.22) days. CONCLUSIONS--The computer advisory system could improve patient management by reducing the time spent receiving ineffective treatment. This has implications for both patient time and clinical costs. 相似文献
105.
106.
The quantitative autoradiographic L-[1-14C]leucine method for the determination of regional rates of cerebral protein synthesis in vivo takes into account recycling of unlabeled leucine derived from protein degradation into the precursor pool for protein synthesis. We have evaluated the degree of recycling by measuring the ratio of the apparent steady-state leucine specific activity in the precursor amino acid pool (tRNA-bound leucine) to that in the arterial plasma. In the whole brain of the conscious rat this ratio (lambda WB) equals 0.58. The equivalent ratio for leucine in the acid-soluble pool in whole brain (psi WB) is 0.49. A first-degree polynomial equation for lambda WB as a function of psi WB was fitted from paired determinations. To determine the degree of recycling in local regions of the brain, we have measured in individual brain regions (i) psi i and calculated lambda i assuming that the fitted equation also applies to these localized regions. Our results indicate that the degree of recycling into the precursor pool does vary regionally; lambda i in the individual regions varies from 0.62 in the hypoglossal nucleus to 0.50 in the globus pallidus. Local rates of protein synthesis were then determined by the autoradiographic technique with regional corrections for recycling of unlabeled leucine. Rates of leucine incorporation into protein averaged 6.1 nmol/g of tissue/min in the brain as a whole, with the rates in gray matter about twice those in white matter. 相似文献
107.
Lymphatic drainage in patients after replantation of extremities 总被引:1,自引:0,他引:1
Lymph drainage was studied by means of lymph scintigraphy in eight patients in whom successful replantation of a totally or subtotally amputated extremity had been performed. Scintigrams were made after subcutaneous injection of technetium-99m in the replanted part of the patient and the contralateral, normal extremity. In all scintigrams, axillary or inguinal lymph node activity is seen, implying drainage of lymph by means of the lymph vessels. Retention of colloid in the replanted part (79 to 94 percent) shows no significant difference with the contralateral, normal side (86 to 94 percent). Unquestionable evidence of regeneration of lymphatics in humans is delivered in the three patients, in whom lymph node activity and normal retention percentages are seen on the scintigrams after total amputation of an extremity followed by replantation without anastomosing of interrupted lymph vessels. 相似文献
108.
109.
B E Woodcock E Smith W H Lambert W M Jones J H Galloway M Greaves F E Preston 《BMJ (Clinical research ed.)》1984,288(6417):592-594
Reports suggest that the low incidence of ischaemic heart disease in Greenlandic Eskimos is related to the effect of a diet rich in eicosapentaenoic acid on platelet reactivity and plasma lipid concentrations. A double blind randomised investigation was therefore conducted of the effects on blood viscosity of dietary supplementation with an oil rich in this fatty acid (1.8 g/day, given as fish oil) and an eicosapentaenoic acid poor oil (as corn/olive oil) in patients with peripheral arterial disease. A statistically significant reduction in whole blood viscosity was observed at seven weeks in those patients receiving the eicosapentaenoic acid rich oil. No changes in plasma viscosity, haemoglobin concentration, packed cell volume, or platelet count were seen. A significant fall in plasma triglyceride concentration was also noted only in the patients receiving oil rich in eicosapentaenoic acid; plasma concentrations of cholesterol and high density lipoprotein cholesterol were unchanged. It is concluded that rheological changes that result from a diet rich in eicosapentaenoic acid may contribute to the suggested protective effects of such a diet against arterial disease and that such changes are of potential therapeutic importance in established arterial disease. 相似文献
110.