全文获取类型
收费全文 | 1286篇 |
免费 | 136篇 |
国内免费 | 1篇 |
出版年
2022年 | 10篇 |
2021年 | 23篇 |
2020年 | 7篇 |
2019年 | 19篇 |
2018年 | 18篇 |
2017年 | 25篇 |
2016年 | 26篇 |
2015年 | 59篇 |
2014年 | 51篇 |
2013年 | 74篇 |
2012年 | 87篇 |
2011年 | 93篇 |
2010年 | 48篇 |
2009年 | 46篇 |
2008年 | 66篇 |
2007年 | 70篇 |
2006年 | 53篇 |
2005年 | 57篇 |
2004年 | 51篇 |
2003年 | 53篇 |
2002年 | 60篇 |
2001年 | 22篇 |
2000年 | 19篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 14篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 16篇 |
1987年 | 19篇 |
1986年 | 9篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 16篇 |
1982年 | 14篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 14篇 |
1966年 | 5篇 |
排序方式: 共有1423条查询结果,搜索用时 171 毫秒
1.
Gastrointestinal pH measurement in rats: influence of the microbial flora, diet and fasting 总被引:1,自引:0,他引:1
The pH of the rat intestinal tract was decreased by the presence of a microbial flora, but its influence in the forestomach is less clear. Stomach pH values varied according to the amount of food present at the time of measurement. Fasting increased the pH of the gastrointestinal tract in conventional rats but had little effect in germfree rats. In the conventional rat, feeding a purified diet compared with a commercial diet resulted in a lower pH in the forestomach and a higher pH in the caecal contents. Magnesium trisilicate promoted gastric emptying in conventional rats and its antacid effect was observed only in the caecum and colon. 相似文献
2.
3.
4.
5.
Effect of Cuticle Treatments on Infection of Phaseolus vulgaris by Rhizoctonia solani 总被引:1,自引:0,他引:1
Rhizoctonia solani, the causal agent of stem canker of beans, does not commonly infect beans more than two weeks old. Treatment of the cuticular layer by abrasion or chloroform rinsing results in decreased cuticular autofluorescence and the ability of stains to penetrate the hypocotyl surface. Infection cushions preferentially formed near these treated areas on both young and old plants. The morphology of infection cushions on older plants is simpler than those found on young, susceptible plants, but they are fully competent to form lesions. 相似文献
6.
In some animals sex is determined after conception by environmental factors (environmental sex determination. ESD). In the amphipod Gammarus duebeni sex is reportedly determined by photoperiod: there is a higher proportion of males in broods reared under long-day than under short-day photoperiods. It has been proposed that this is an adaptive response to seasonal population dynamics. A test of the hypothesis would be to demonstrate changes in the degree to which sex is determined by the environment in populations from different latitudes with different dynamics. This study reports such a test. Environmental response is significantly less strong in a southern population with a long breeding season than in a northern one in which breeding is seasonally restricted. Moreover, the threshold of the ESD cue for male or female determination is not defined when the breeding season is weakly seasonal. There is a broad correlation between latitude (and hence breeding seasonality) and the strength of ESD response across a series of population studies. Similarities between the Gammarus system of sex determination and that of the Atlantic silverside Menidia menidia, a fish with thermal ESD, are discussed. 相似文献
7.
Robert M. Levin Penelope A. Longhurst Sheila S. Levin Niels Haugaard Alan J. Wein 《Molecular and cellular biochemistry》1990,97(2):153-159
The urinary bladder depends on intracellular ATP for the support of a number of essential intracellular processes including contraction. The concentration of ATP is maintained constant primarily via the rapid transfer of a phosphate from creatine phosphate (CP) to ADP catalyzed by the enzyme creatine kinase (CK). Since muscular pathologies associated with diabetes are in part related to intracellular alterations in metabolism, we have characterized the CK activity in both skeletal muscle and urinary bladder from control and streptozotocin-diabetic rats.The following is a summary of the results: 1) Bladder tissue from control rats showed linear kinetics with a Vmax = 390 nmoles/mg protein/min, and a Km = 275 µM. 2) Urinary bladder tissue isolated from diabetic rats displayed biphasic kinetics with Vmax = 65 and 324 nmoles/mg protein/min, and Km's = 10 µM and 190 µM respectively. 3) Skeletal muscle isolated from control rats showed linear kinetics with an approximate Vmax of 800 nmoles/mg protein/min and a Km of 280 µM CP. 4) Homogenates of skeletal muscle from diabetic rats showed complex kinetics not separable into distict component forms. 5) The Km for ADP for both skeletal muscle and bladder was approximately 10 µM.These studies demonstrate that whereas bladders isolated from both control and diabetic rats possess a low-affinity isomer(s) of CK with similar maximum enzymatic activity, there is a high affinity isomer present within the urinary bladder muscle of diabetic rats that is not present in bladder tissue isolated from control rats. Skeletal muscle isolated from both diabetic and control rats exhibited a maximal activity 2 to 3 times higher than that of the bladder. 相似文献
8.
Timothy D. Noakes Estelle V. Lambert Michael I. Lambert Penelope S. McArthur Kathryn H. Myburgh A. J. Spinndler Benade 《European journal of applied physiology and occupational physiology》1988,57(4):482-489
Two studies were undertaken to characterize the effects of carbohydrate ingestion on fuel/hormone response to exercise and muscle glycogen utilization during prolonged competitive exercise. In study 1, eighteen subjects were divided into three groups, matched for maximum oxygen consumption (VO2max) and blood lactate turnpoint. All subjects underwent a 3-day carbohydrate (CHO) depletion phase, followed by 3 days of CHO loading (500-600 g.day-1). During the race, the groups drank either 2% glucose (G), 8% glucose polymer (GP), or 8% fructose (F). Muscle biopsies were performed before and after the race and venous blood was sampled before and at regular intervals during the race. In study 2, eighteen subjects divided into 2 matched groups ingested either a 4% G or 10% GP solution during a 56 km race. Despite significantly greater CHO ingestion by GP and F in study 1 and by GP in study 2, blood glucose, free fatty acids and insulin concentrations, muscle glycogen utilization and running performance were not different between groups. These studies show (i) that hypoglycaemia is uncommon in athletes competing in races of up to 56 km provided they CHO-load before and ingest a minimum of 10 g CHO.h-1 during competition; (ii) that neither the amount (10 g vs 40 g.h-1) nor the type of carbohydrate (G vs GP vs F) has any effect on the extent of muscle glycogen depletion or running performance in matched subjects racing over distances up to 56 km. 相似文献
9.
Davis G. M.; Coates A. L.; Papageorgiou A.; Bureau M. A. 《Journal of applied physiology》1988,65(3):1093-1098
The measurement of pulmonary mechanics has been developed extensively for adults, and these techniques have been applied directly to neonates and infants. However, the compliant chest wall of the infant frequently predisposes to chest wall distortion, especially when there is a low dynamic lung compliance (CL,dyn). We describe a technique of directly measuring the static chest wall compliance (Cw,st), developed initially in the newborn lamb and subsequently applied to the premature neonate with chest wall distortion. The mean CL,dyn in seven intubated newborn lambs in normoxia was 2.45 +/- 0.41 ml.cmH2O-1.kg-1, whereas Cw,st was 11.81 +/- 0.25 ml.cmH2O-1.kg-1. These values did not change significantly in seven animals breathing through a tight-fitting face mask or with hypercapnia-induced tachypnea. For the eight premature infants the mean CL,dyn was 1.35 +/- 0.36 ml.cmH2O-1.kg-1, whereas the mean Cw,st was 3.16 +/- 1.01 ml.cmH2O-1.kg-1. This study shows that, under relaxed conditions when measurements of static compliance are performed, the chest wall is more compliant than the lung. The measurement of Cw,st may thus be used to determine the contribution of the respiratory musculature in stabilizing the chest wall. 相似文献
10.
Stephen F. Lincoln Andrea M. Hounslow Bruce G. Doddridge John M. Coates 《Inorganica chimica acta》1985,100(2):207-210
Proton NMR studies of N,N-diethylformamide (def) exchange on [M(Me6tren)def]2+ where M = Co and Cu yield: kex (298.2K) = 26.3 ± 2.2, 980 ± 70 s−1; ΔH≠ = 58.3 ± 1.7, 36.3 ± 0.9 kJ mol−1; ΔS≠= −22.2 ± 4.6, −65.9 ± 2.5 J K−1 mol−1; and ΔV≠ = −1.3 ± 0.2, 5.3 ± 0.3 cm3 mol−1 respectively. These data which are consistent with a and d activation modes operating when M = Co and Cu respectively are compared with data for related systems. 相似文献