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   6944篇
  免费   88篇
  国内免费   2篇
电工技术   72篇
综合类   1篇
化学工业   661篇
金属工艺   85篇
机械仪表   91篇
建筑科学   169篇
矿业工程   17篇
能源动力   83篇
轻工业   470篇
水利工程   53篇
石油天然气   16篇
无线电   605篇
一般工业技术   749篇
冶金工业   3262篇
原子能技术   39篇
自动化技术   661篇
  2021年   43篇
  2020年   30篇
  2019年   65篇
  2018年   68篇
  2017年   50篇
  2016年   51篇
  2015年   41篇
  2014年   69篇
  2013年   211篇
  2012年   119篇
  2011年   174篇
  2010年   126篇
  2009年   123篇
  2008年   178篇
  2007年   179篇
  2006年   160篇
  2005年   142篇
  2004年   119篇
  2003年   108篇
  2002年   112篇
  2001年   117篇
  2000年   97篇
  1999年   158篇
  1998年   842篇
  1997年   547篇
  1996年   350篇
  1995年   260篇
  1994年   252篇
  1993年   242篇
  1992年   108篇
  1991年   92篇
  1990年   113篇
  1989年   121篇
  1988年   90篇
  1987年   107篇
  1986年   90篇
  1985年   98篇
  1984年   75篇
  1983年   64篇
  1982年   66篇
  1981年   56篇
  1980年   69篇
  1979年   61篇
  1978年   58篇
  1977年   114篇
  1976年   235篇
  1975年   54篇
  1974年   37篇
  1973年   37篇
  1972年   36篇
排序方式: 共有7034条查询结果,搜索用时 0 毫秒
991.
Tick-borne diseases in the United States   总被引:1,自引:0,他引:1  
  相似文献   
992.
993.
We tested the influence of in vivo volume resuscitation on intrinsic contractile properties of left ventricular (LV) preparations of endotoxemic guinea pigs. Escherichia coli endotoxin (LPS)-injected animals were divided into nonresuscitated and resuscitated groups. Volume resuscitation improved cardiac output and stroke volume, increased arterial pH and body temperature, and decreased mortality. In isovolumetric LV preparations isolated 4 h after LPS injection, LV systolic pressures (in mmHg) preparations isolated 4 h after LPS injection, LV systolic pressures (in mmHg) of LPS with (42 +/- 3) and without (42 +/- 2) fluid resuscitation were consistently less than control values (70 +/- 3). LV end-diastolic pressure-volume (compliance) decreased in LPS-nonresuscitated hearts, while LV compliance of LPS-resuscitated hearts was similar to control. Thus, intravascular volume expansion selectively improved LV diastolic compliance of LPS hearts without affecting LV systolic function. These findings suggest that LV systolic and diastolic dysfunctions associated with endotoxemia and Gram-negative sepsis may involve separate pathogenic mechanisms.  相似文献   
994.
INTRODUCTION: Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal dominant condition characterized by early age of onset colorectal cancer, right-sided predominance, excess of synchronous and metachronous colonic neoplasms, and extracolonic cancers. The purpose of this study is to report clinical characteristics of HNPCC families in our registry. METHODS: This is a retrospective review of medical records of patients with a significant history of colorectal cancer and interviews with their families. RESULTS: Three hundred one people with cancer in 40 HNPCC families were identified. In 284 of 301 (94 percent) people, 363 cancers were identified. Colorectal cancer only was identified in 182 people (64 percent) and, in conjunction with extracolonic tumors, in another 31 people (11 percent). Extracolonic cancer alone was noted in 71 people (25 percent). Median age at diagnosis of colorectal cancer was 48 (range, 17-92) years. In patients with documented pathology, right-sided tumors predominated (55 percent), synchronous and metachronous tumors were noted in 53 percent, and synchronous of metachronous adenomas were documented in 51 percent of people. Generational anticipation was also noted. CONCLUSION: This study demonstrates and confirms characteristics that have been described in HNPCC. Namely, early age of onset of colorectal cancer, right-sided predominance, multiple synchronous and metachronous neoplasms, increased extracolonic cancers, and generational anticipation.  相似文献   
995.
Citrate, when activated by a water-soluble carbodiimide, covalently modifies hemoglobin. At pH values near neutrality, complete modification of the N-terminal valine residues of alpha- and beta-globin chains can be accomplished with a high degree of specificity. These groups react at a much more rapid rate than a slower reacting set of functional groups. Modification of hemoglobin with citrate alters the oxygen affinity of the protein. Although the p50 is not changed, the cooperative nature of oxygen binding is greatly decreased. Hemoglobin S modified with citrate is more soluble than unmodified hemoglobin S. The time taken for deoxygenated hemoglobin S to come out of solution in concentrated phosphate solutions is increased by citrate modification.  相似文献   
996.
997.
BACKGROUND: The major problems after pterygium removal are recurrence and complications of the therapy. The authors investigated a simple surgical treatment without adjunctive therapy for primary pterygium. METHODS: Patients eligible to be included in the study were identified from a pterygium treatment log. They represent consecutive cases over a 6 1/2-year period, all of whom had been treated by one surgeon using a superior, sliding, conjunctival flap to cover the pterygium defect. An attempt was made to obtain follow-up of at least 1 year for each patient. RESULTS: Two hundred fifty-eight eyes in 236 patients were included in the study. Two hundred twenty-two eyes (86%) were able to be followed by either record review or re-examination. Seven pterygia (3.2%) recurred, all identified by record review, with no recurrences identified by re-examination. Recurrences were more likely after early postoperative flap retraction (5 of 7 recurrences) and recurrence occurred at a mean interval of 4.3 months (range, 1.5-11 months) after surgery. Symptomatically, the patients were comfortable, and the cosmetic result was good. CONCLUSION: This study indicates that this simple surgical procedure for the treatment of primary pterygium should be evaluated further by controlled clinical trials.  相似文献   
998.
Dendritic cell-based immunotherapy of prostate cancer   总被引:1,自引:0,他引:1  
The protective effect of catechins, major components of green tea, was studied in cultured human umbilical vein endothelial cells exposed to toxicity induced by linoleic acid hydroperoxide (LOOH). In the case where cells were incubated in medium containing both LOOH and catechins, (+)-catechin (C) was effective in suppressing of LOOH-induced cytotoxicity, but (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG) had no effect. EGCG monoglucoside (EGCG-G1) and EGCG diglucoside (EGCG-G2), apophilic derivatives of EGCG, show a protective effect on LOOH-induced cytotoxicity when present at the time of treatment with LOOH. On the other hand, when cells were incubated with catechins for 24 h before treatment with LOOH there was no protection against the oxidative damage by LOOH. Furthermore, the interaction between catechins and alpha-tocopherol was examined under these culture conditions. C showed a synergistic effect with alpha-tocopherol in protecting against LOOH-induced damage. These results suggest that catechins interact with LOOH present in the medium or near the surface of membranes, but not with LOOH incorporated into cellular membranes and that catechins are able to interact with alpha-tocopherol to provide synergistic protection against the cytotoxicity of LOOH.  相似文献   
999.
1000.
The study of the underground parts of plants is often difficult, and as a result roots are often treated as homogeneous physiological entities with respect to root respiration. In this study we demonstrate a partitioning of respiration within root tissues using nitro blue tetrazolium staining and an incident light optical system that permits detailed observations of intact roots. The assay is rapid and easy to perform, and reveals that respiratory activity in roots is not uniform in space and time. The results show that root hairs in particular may be regions of enhanced respiratory activity in some species or in certain developmental or physiological states. This fact has important implications for the role of root hairs in the overall respiratory budget of roots and the energetics of nutrient assimilation. The results suggest that root respiration studies should consider differential respiratory activities of root cell types within roots.  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