全文获取类型
收费全文 | 2591篇 |
免费 | 205篇 |
出版年
2023年 | 11篇 |
2022年 | 17篇 |
2021年 | 45篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 35篇 |
2017年 | 40篇 |
2016年 | 45篇 |
2015年 | 99篇 |
2014年 | 111篇 |
2013年 | 137篇 |
2012年 | 187篇 |
2011年 | 173篇 |
2010年 | 113篇 |
2009年 | 128篇 |
2008年 | 144篇 |
2007年 | 158篇 |
2006年 | 142篇 |
2005年 | 128篇 |
2004年 | 123篇 |
2003年 | 122篇 |
2002年 | 96篇 |
2001年 | 41篇 |
2000年 | 27篇 |
1999年 | 27篇 |
1998年 | 26篇 |
1997年 | 16篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 9篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1990年 | 26篇 |
1989年 | 21篇 |
1988年 | 20篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 18篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 17篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1974年 | 16篇 |
1973年 | 13篇 |
1972年 | 14篇 |
1971年 | 9篇 |
1968年 | 11篇 |
排序方式: 共有2796条查询结果,搜索用时 15 毫秒
1.
Analogs of the molluscan neuropeptide FMRFamide were tested on four different molluscan muscle preparations which show qualitatively different responses to the peptide; the structure-activity relations are basically similar, but not identical. The C-terminal amide and the Arg3 residue are critical for FMRFamide-like activity on all four preparations. In contrast, analogs extended at the N-terminal or with conservative substitutions for the Phe1 or Met2 residue are approximately equipotent to FMRFamide. These structural requirements parallel those for the C-terminal tetrapeptide amide of gastrin. 相似文献
2.
Detailed methods are presented for measurement and study of in vivo mutations and in vitro mutagenesis in human lymphocytes. The methods described include preparation of conditioned medium containing interleukin-2, enumeration of mutant clones, in vitro mutagenesis, and expansion of mutant clones for further study. 相似文献
3.
4.
Effects of opioid blockade with nalmefene in older impotent men 总被引:2,自引:0,他引:2
We evaluated the effect of the opioid antagonist nalmefene on the HPG axis and on food consumption in 14 older impotent men. These patients had low to low normal mean serum testosterone values and normal gonadotrophin levels on screening evaluation. Normal response to GnRH was demonstrated in all the men. The protocol called for 24 hours of evaluation before and during administration of nalmefene 2.0 mg IV every 8 hours for 3 doses. During each 24 hour period, the following determinations were made: serum testosterone, FSH, and LH by five separate determinations between 8 AM and noon; 8 AM and 11 PM serum cortisols; 24 hour urine collections for free cortisol; and nocturnal penile tumescence (NPT). Food consumption was measured from 4 PM to 10 AM during the two periods. Nalmefene resulted in significant rises in testosterone, LH, and FSH. Nalmefene significantly elevated morning and evening cortisol measurements in all the patients. Nalmefene decreased total calorie consumption, principally by decreasing fat consumption. There was no effect on NPT. We conclude that in older impotent men, nalmefene acutely increases activity of the HPG axis and decreases calorie intake predominantly by decreasing fat consumption. 相似文献
5.
Iain J. Mcgaw 《Marine and Freshwater Behaviour and Physiology》2006,39(2):131-141
Cardiovascular and respiratory variables were recorded in the blue crab, Callinectes sapidus, during injury and subsequent autotomy of a chela. Cardiac function and haemolymph flow rates were measured using a pulsed-Doppler flowmeter. Oxygen uptake was recorded using an intermittent flow respirometry system. Crabs reacted to the loss of a chela with a rapid increase in heart rate, which was sustained for 2 h. Stroke volume of the heart also increased after the chela was autotomized. A combined increase in heart rate and stroke volume led to an increase in cardiac output, which was maintained for an hour after the loss of a chela. There was also differential haemolymph perfusion of various structures. There was no change in perfusion of the anterolateral arteries or posterior and anterior aortae, during injury of the chela or subsequent autotomy. Haemolymph flow rates did increase significantly through the sternal artery during injury and immediately following autotomy of the chela. This was at the expense of blood flow to the digestive gland: a sustained decrease in haemolymph flow through the hepatic arteries occurred for 3 h following autotomy. Fine-scale cardiac changes associated with the act of autotomy included a bradycardia and/or associated cardiac pausing before the chela was shed, followed by a subsequent increase in cardiac parameters. Changes in the cardiovascular physiology were paralleled by an increase in oxygen uptake, which was driven by an increased ventilation of the branchial chambers. Although limb loss is a major event, it appears that only acute changes in physiology occur. These may benefit the individual, allowing rapid escape following autotomy with a subsequent return to normal activity. 相似文献
6.
Exposure of human lymphocytes to ionizing radiation reduces mutagenesis by subsequent ionizing radiation 总被引:3,自引:0,他引:3
The effect of prior incubation with [3H]thymidine on survival and mutagenesis after X-irradiation of human lymphocytes was studied by incubating lymphocytes with 0.001-1.0 mu Ci/ml [3H]thymidine for 6 h at 37 degrees C and then irradiating with 150 or 300 rad. Survival was measured using lymphocyte cloning and mutagenesis was measured using 6-thioguanine selection to detect clones mutated at the hypoxanthine phosphoribosyltransferase locus. [3H]Thymidine alone had no effect on survival or mutagenesis and X-radiation alone produced the expected decrease in survival and increase in mutations. [3H]Thymidine prior to X-radiation had no effect on lethality of X-radiation but at concentrations of 0.1 and 1.0 mu Ci/ml produced a significant decrease in the number of mutations induced after both 150 and 300 rad. The results suggest that ionizing radiation, produced by disintegration of 3H, reduces the mutagenic effect of a subsequent exposure to ionizing radiation by induction of a system which prevents or repairs a restricted class of radiation damage. 相似文献
7.
Iain Mattaj 《Disease models & mechanisms》2008,1(1):16-Aug;1(1):16
8.
9.
Alexander A. Morley 《Journal of theoretical biology》1982,98(3):469-474
A number of unexplained features of ageing can be accounted for if cellular ageing is due to dominant or co-dominant mutations. The experimental evidence both for and against this hypothesis is weak, but experiments involving direct testing are possible. 相似文献
10.