首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   296506篇
  免费   2461篇
  国内免费   621篇
电工技术   4439篇
综合类   2453篇
化学工业   43183篇
金属工艺   18725篇
机械仪表   12735篇
建筑科学   5941篇
矿业工程   2974篇
能源动力   4378篇
轻工业   12795篇
水利工程   4525篇
石油天然气   9954篇
武器工业   12篇
无线电   27666篇
一般工业技术   66557篇
冶金工业   34269篇
原子能技术   7917篇
自动化技术   41065篇
  2018年   21724篇
  2017年   21282篇
  2016年   15545篇
  2015年   2685篇
  2014年   3335篇
  2013年   6770篇
  2012年   8894篇
  2011年   19582篇
  2010年   17469篇
  2009年   14846篇
  2008年   15693篇
  2007年   17937篇
  2006年   4361篇
  2005年   7549篇
  2004年   6161篇
  2003年   5871篇
  2002年   4474篇
  2001年   3642篇
  2000年   3663篇
  1999年   3313篇
  1998年   7106篇
  1997年   5214篇
  1996年   3891篇
  1995年   2956篇
  1994年   2641篇
  1993年   2762篇
  1992年   2297篇
  1991年   2360篇
  1990年   2417篇
  1989年   2322篇
  1988年   2329篇
  1987年   2199篇
  1986年   2255篇
  1985年   2305篇
  1984年   2214篇
  1983年   2147篇
  1982年   1985篇
  1981年   2200篇
  1980年   2064篇
  1979年   2269篇
  1978年   2433篇
  1977年   2433篇
  1976年   3105篇
  1975年   2246篇
  1974年   2309篇
  1973年   2345篇
  1972年   2159篇
  1971年   1912篇
  1970年   1702篇
  1969年   1696篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
961.
Here we present a case of a patient with a massive ossification of annulus fibrosus and longitudinal ligament at the level C3-C4, C4-C5 and C5-C6, also called the Van Swaay bridge. One can observe a propulsion of the pharingeal tissue at the level of the massive Van Swaay bridge between C5 and C6 which caused pressure and dysphagia.  相似文献   
962.
We investigated changes in the anterior tibial muscle during lengthening of the lower leg in rabbits. In 37 rabbits, an osteotomy of the right middle tibia was performed and was fixed by a unilateral external fixator. The rabbits were randomized into 6 groups. In groups 1, 2, and 3 the tibiae were distracted 0.5 mm/day. In groups 1 and 2, the rabbits were killed after 14 and 28 days of distraction, respectively, and in group 3 after 28 days of distraction, followed by 14 days of rest. Groups 1a, 2a, and 3a served as controls. They were treated similarly as groups 1, 2, and 3, but no distraction was performed. Proliferating cell nuclei were labeled with 5-bromo-2-deoxyuridine and were identified by immunohistochemical staining. The weight of the muscle was measured. During bone lengthening the muscle showed signs of growth, as indicated by increasing weight and number of proliferating cell nuclei. This was observed only during lengthening and it ceased when the lengthening was stopped.  相似文献   
963.
An outbreak of Cryptosporidiosis occurred over three months in a British Columbia community, peaking in December 1990. Results of the case-control study and illness surveys support the hypothesis that transmission occurred in a public children's pool at the local recreation centre. Analysis using lab-confirmed cases revealed a matched odds ratio of 4.5 [95% CI 0.97, 20.83], and using clinical cases an unmatched odds ratio of 12.8 [95% CI 3.68, 46.77], associated with swimming in the children's pool within two weeks prior to onset of illness. Other risk factors were not significant. Attack rates in various groups of children's pool users ranged from 8% to 78%. The children's pool was closed for steam cleaning and disinfection. Unusually frequent defecations including liquid stools had occurred before and during the outbreak. Improvements were instituted for removal of feces and superchlorination of pool water.  相似文献   
964.
For psychological reasons, coelocentesis was performed in 20 women prior to termination of pregnancy, at 6-11 weeks of gestation. The fetal heart rate (FHR) was measured immediately before the procedure and at 1, 5, and 10 min afterward. There was no significant difference between FHR before coelocentesis compared to the values at 1 min (mean = 158, range 114-178; z = -0.629, P = 0.529), 5 min (mean = 160, range 121-179; z = -0.191, P = 0.848), or 10 min (mean 159, range 117-183; z = -0.214, P = 0.83) after the procedure. These findings suggest that coelocentesis does not have a major effect on the fetal cardiovascular system.  相似文献   
965.
EHNA (Erythro-9-[2-hydroxy-3-nonyl]adenine) is a wellknown inhibitor of adenosine deaminase. Recently, EHNA was shown to block the activity of purified soluble cGMPstimulated phosphodiesterase (PDE2) from frog, human, and porcine heart with an apparent Ki value of approximately 1 microM and with negligible effects on Ca2+/calmodulin PDE (PDE1), cGMP-inhibited PDE (PDE3), and low Km cAMP-specific PDE (PDE4) (Méry, P.F., C. Pavoine, F. Pecker, and R. Fischmeister. 1995. Mol. Pharmacol. 48:121-130; Podzuweit, T., P. Nennstiel, and A. Muller. 1995. Cell. Signalling. 7:733- 738). To investigate the role of PDE2 in the regulation of cardiac L-type Ca2+ current (ICa), we have examined the effect of EHNA on ICa in freshly isolated human atrial myocytes. Extracellular application of 0.1-10 microM EHNA induced an increase in the amplitude of basal ICa ( approximately 80% at 1 microM) without modification of the current-voltage or inactivation curves. The maximal stimulatory effect of EHNA on ICa was comparable in amplitude with the maximal effect of isoprenaline (1 microM), and the two effects were not additive. The effect of EHNA was not a result of adenosine deaminase inhibition, since 2'-deoxycoformycin (1-30 microM), another adenosine deaminase inhibitor with no effect on PDE2, or adenosine (1-10 microM) did not increase ICa. In the absence of intracellular GTP, the substrate of guanylyl cyclase, EHNA did not increase ICa. However, under similar conditions, intracellular perfusion with 0.5 microM cGMP produced an 80% increase in ICa. As opposed to human cardiomyocytes, EHNA (1-10 microM) did not modify ICa in isolated rat ventricular and atrial myocytes. We conclude that basal ICa is controlled by PDE2 activity in human atrial myocytes. Both PDE2 and PDE3 may contribute to keep the cyclic nucleotides concentrations at minimum in the absence of adenylyl and/or guanylyl cyclase stimulation.  相似文献   
966.
The internal anal sphincterotomy operation represents the best therapy for the treatment of those anal lesions, above all anal fissures, which cause hypertrophy and spasms of the internal anal sphincter. The Authors report their experience of 253 operations of internal subcutaneous sphincterotomy carried out between 1989 and 1995 under local anaesthesia in the outpatient clinic. The excellent results achieved prove that the procedure can easily be carried out under local anaesthesia in an outpatient clinic and, therefore, it is preferable to the surgical technique of isolation of the internal sphincter, not only for its practicality but also for the improved results.  相似文献   
967.
968.
The effects of the competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, LY235959, were determined on the analgesic and hypothermic effects as well as on the development of tolerance to these effects of U-50,488H, a kappa-opioid receptor agonist in mice and rats. In the mouse, a single injection of LY235959 given 10 min prior to U-50,488H did not modify the analgesic action of the latter. Similarly, chronic administration of LY235959 twice a day for 4 days did not modify U-50,488H-induced analgesia in mice. Repeated pretreatment of mice with LY235959 dose-dependently attenuated the development of tolerance to the analgesic actions of U-50,488H. In the rat, LY235959 by itself produced a significant analgesia and prior treatment of rats with LY235959 enhanced the analgesic action of U-50,488H. Similar effects were seen with the hypothermic action. Pretreatment of rats with LY235959 attenuated the development of tolerance to the analgesic but not to the hypothermic action of U-50,488H. These results provide evidence that LY235959 produces differential actions on nociception and thermic responses by itself and when given acutely with U-50,488H in mice and rats. However, when the animals are pretreated with LY235959, similar inhibitory effects are observed on the development of tolerance to the analgesic action of U-50,488H in both the species. These studies demonstrate an involvement of the NMDA receptor in the development of kappa-opioid tolerance and suggest that the biochemical consequences of an opioid's interaction with the opioid receptor are not the only factors that contribute to the acute and chronic actions of opioid analgesic drugs.  相似文献   
969.
New liquid UHT milks supplemented with iron (0.9-1.4 mg/100 ml), vitamin C (1-7 mg/100 ml), lactose (2-4 g/100 ml) and linoleic acid (200-400 mg/100 ml), named growth milks, have recently become available to satisfy the specific nutritional needs of children aged 1-3 years. But the iron-vitamin C mixture could activate the lactose-induced Maillard reaction and tryptophan (Trp) oxidation in proteins. We have therefore examined the Amadori product and Trp concentrations of these milks. Forty-two commercial growth milks from five firms were analysed for the Maillard reaction and the soluble protein Trp content and compared with 64 UHT milks. The furosine concentration of total proteins was two to four times higher in 'growth' milks than in standard UHT milks, indicating a proportional loss of available lysine. The Trp fluorescence of undenatured proteins soluble at pH 4.6 was almost three times lower in 'growth' than in standard milks and Trp concentration 36% lower suggesting destruction of this oxidation-sensitive amino-acid. The mechanism of Trp destruction remains to be elucidated, and the roles of iron and Amadori products determined.  相似文献   
970.
The objective of this survey was to demonstrate whether a primary care track internal medicine residency program emphasizing community-based health care of the urban sick poor trains physicians who will continue to practice in general internal medicine or similar fields. Thirty-five primary care residents (100% of graduates) who trained from 1976 through 1993 in the Adult Primary Care Track of the Internal Medicine Residency Program at St. Vincent's Hospital, New York were used as participants.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号