全文获取类型
收费全文 | 6477篇 |
免费 | 672篇 |
国内免费 | 4篇 |
专业分类
7153篇 |
出版年
2022年 | 38篇 |
2021年 | 85篇 |
2020年 | 53篇 |
2019年 | 63篇 |
2018年 | 88篇 |
2017年 | 68篇 |
2016年 | 129篇 |
2015年 | 197篇 |
2014年 | 237篇 |
2013年 | 310篇 |
2012年 | 399篇 |
2011年 | 406篇 |
2010年 | 247篇 |
2009年 | 263篇 |
2008年 | 341篇 |
2007年 | 376篇 |
2006年 | 294篇 |
2005年 | 339篇 |
2004年 | 295篇 |
2003年 | 304篇 |
2002年 | 281篇 |
2001年 | 117篇 |
2000年 | 135篇 |
1999年 | 125篇 |
1998年 | 119篇 |
1997年 | 82篇 |
1996年 | 82篇 |
1995年 | 63篇 |
1994年 | 83篇 |
1993年 | 74篇 |
1992年 | 80篇 |
1991年 | 72篇 |
1990年 | 78篇 |
1989年 | 92篇 |
1988年 | 85篇 |
1987年 | 77篇 |
1986年 | 61篇 |
1985年 | 56篇 |
1984年 | 59篇 |
1983年 | 60篇 |
1982年 | 49篇 |
1981年 | 51篇 |
1980年 | 54篇 |
1979年 | 44篇 |
1978年 | 46篇 |
1976年 | 37篇 |
1975年 | 43篇 |
1974年 | 45篇 |
1973年 | 48篇 |
1969年 | 40篇 |
排序方式: 共有7153条查询结果,搜索用时 0 毫秒
71.
The reversal of phenylarsenoxide inhibition of keto acid oxidation in mitochondrial and bacterial suspensions by lipoic acid and other disulphides 总被引:2,自引:1,他引:1 下载免费PDF全文
1. Inhibition of pyruvate oxidation in suspensions of Aerobacter aerogenes cells and of isolated mitochondria from rat heart and liver by phenylarsenoxide is prevented by an excess of lipoic acid, whereas inhibition due to certain bivalent cations is not. 2. In both systems inhibition persists when the bacteria and mitochondria are recovered and resuspended in fresh media in the absence of the inhibitor. Persistent inhibition due to preincubation with phenylarsenoxide, but not with the metal ions, is reversed by lipoic acid and by certain other disulphides. 3. 2,3-Dimercaptopropan-1-ol prevents the inhibition of pyruvate oxidation by phenylarsenoxide and by bivalent cations in both mitochondria and bacterial cells. 4. In aerobic suspensions of mitochondria and bacteria disulphides such as lipoic acid are reduced rapidly to dithiols. Reduction is inhibited by Co(2+), Ni(2+), Cd(2+) and Zn(2+), but not by phenylarsenoxide. 5. It is concluded that the inability of lipoic acid to prevent the action of the metal ions on pyruvate oxidation is due to the inhibition of its reduction to the effective dithiol. 相似文献
72.
73.
74.
75.
Ring cleavage of atrial natriuretic peptide (ANF) between Cys7 and Phe8 by endoprotease 3.4.24.11 yields X-ANF. Since endoprotease 3.4.24.11 may contribute to ANF metabolism in vivo, the present study determined if X-ANF exhibits reduced biological activity in comparison to the parent molecule. 相似文献
76.
D. E. Neal P. D. Ramsden L. Sharples A. Smith P. H. Powell R. A. Styles R. J. Webb 《BMJ (Clinical research ed.)》1989,299(6702):762-767
OBJECTIVES--To determine the symptomatic and urodynamic outcome of elective prostatectomy and to establish whether the outcome is influenced or can be predicted by preoperative urodynamic measurements. DESIGN--Prospective non-randomised study with follow up at a mean of 11 months after operation. Most men were assessed jointly by a urologist and a general practitioner. SETTING--Department of urology in a teaching hospital serving a large district population. PATIENTS--253 Men listed for elective prostatectomy because of symptoms and low urinary flow rates (less than 15 ml/s) and excluding those already on a waiting list or with acute urinary retention, clinically apparent prostatic cancer, and neurological or cerebrovascular disease; 217 (86%) were followed up. INTERVENTION--Elective prostatectomy. MAIN OUTCOME MEASURE--Classification on the basis of relief of symptoms assessed by patients and urologist and general practitioner and of symptom scores obtained by questionnaire. RESULTS--Of the 217 men followed up, 171 (79%) had a satisfactory subjective review and 155 (72%) had a satisfactory review and also low symptom scores. An unsatisfactory outcome was associated with preoperative symptoms of urge incontinence, small prostatic size and resected weight, low voiding pressures, and low urethral resistance. Preoperative maximum urinary flow rates did not predict outcome. Men with poor outcome could be classified into two groups: those with irritative symptoms who were more likely before operation to have had urge incontinence and detrusor instability and men with symptoms of poor urinary flow who were more likely before operation to have had a small prostate, low voiding pressures, and low urethral resistance. In patients in the second group flow rates or voiding pressures improved little after operation. Men with stable detrusors and either low urethral resistance or low voiding pressures were less likely to do well after prostatectomy, but despite these associations preoperative urodynamic measurements were unable to predict outcome accurately. CONCLUSIONS--Prostatectomy was satisfactory in relieving symptoms and improving urodynamic measurements in most men, but even in those with classic symptoms and low urinary flow rates a substantial minority experienced little improvement afterwards and urodynamic measurements did not accurately predict outcome in individual patients. 相似文献
77.
78.
The aims of this study were to investigate whether treatment with a single ovulatory dose of hCG, between the day of oestrus and the end of the luteal phase, could induce extra ovulations in heifers and whether the presence of an existing corpus luteum (CL) affected the response. Heifers (N = 32) were injected with 1500 i.u. hCG or saline on a given day of the oestrous cycle. Treatments were repeated during subsequent cycles to provide a total of 71 observations, 57 of which followed an injection of hCG, given between Day 0 (oestrus) and Day 16, and 14 of which followed saline injections as controls. Ovulatory responses were noted by laparoscopy 2 days after hCG treatment. No heifers injected with saline produced additional CL. Of the hCG-treated cycles, 23 resulted in the formation of an additional CL, and this was significantly affected by the stage of the oestrous cycle when hCG was given; a greater response was observed during the early (Days 4-7) and late (Days 14-16) stages of the luteal phase than at the mid-luteal phase of the oestrous cycle. Two heifers were also treated with hCG on Days 17 or 18 of the oestrous cycle, but before oestrus; both had induced CL. There were no significant differences between the left-right orientation of the existing CL or the hCG-induced CL. These results demonstrate that the large, luteal-phase follicle of the cow is capable of ovulating in response to hCG and that the induced CL is not affected by the presence of an existing CL. 相似文献
79.
Dilator actions of endothelin in coronary resistance vessels and the abdominal aorta of the guinea pig 总被引:3,自引:0,他引:3
Endothelin has been characterized as a potent constricting factor. The purpose of this study was to investigate possible dilator effects of this peptide and to examine whether dilator responses occur through an endothelium-mediated mechanism in guinea pig coronary resistance vessels and isolated aortic rings. Changes in perfusion pressure after bolus injections of endothelin were measured using a constant-flow modified Langendorff preparation with a transducer between the flow pump and the heart. An immediate fall in perfusion pressure, averaging 6 mmHg, was observed after injection of endothelin (10(-14)-10(-12) moles). This effect was maximal at 1 minute and tended to return toward baseline levels within 4 minutes. In response to endothelin (10(-9) M), isolated aortic rings relaxed 35% after being contracted with prostaglandin F2 alpha (10(-7) M). In both preparations, dilation was converted to constriction after endothelium damage by oxygen radicals or endothelium removal (mechanical rubbing). Dilator responses to endothelin were blocked by pretreatment for 30 minutes with indomethacin (14 microM) in the presence of an intact endothelium in coronary resistance vessels, whereas in the abdominal aorta they were not. We conclude that endothelin has significant dilator properties and that this effect is opposed by its constrictor action at higher doses. In addition, dilator responses to endothelin require an intact endothelium in both coronary vessels and abdominal aorta. Finally, endothelin-induced dilation in coronary resistance vessels appears to occur through a cyclooxygenase product-mediated mechanism. 相似文献
80.
Predation on Protozoa: its importance to zooplankton 总被引:34,自引:0,他引:34
Protozoa are an important component of both the nano- and microplanktonin marine and freshwater environments and are preyed upon byzooplankton, including suspension-feeding cope pods, some gelatinouszoopiankters and some first-feeding fish larvae. The clearancerates of suspension-feeding zooplankton for ciliates, in particular,are higher than for most phytoplankton. For at least some suspension-feedingzooplankton, protozoans are calculated to be quantitativelyan important component of the diet during certain seasons. Inlaboratory studies, protozoan components in the diet appearto enhance growth and survival of certain life-history stagesor enhance fecundity. These data suggest that protozoans arequalitatively as well as quantitatively important in the dietsof marine zooplankton. Most studies of predation on Protozoahave focused on the euphotic zone in nearshore waters. Predationon Protozoa is expected, however, to be particularly importantboth quantitatively and qualitatively in marine environmentsand seasons in which primary production is dominated by cells<5 µm in size, such as nearshore environments afterthe spring phytoplankton bloom, in oligotrophic waters, andin environments dominated by detritus-dominated food webs, suchas the deep sea. In detritus-dominated food webs, Protozoa maybe a source of essential nutrients and may thus facilitate utilizationof bacterial and detrital carbon by metazoan plankton. 相似文献