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   3262篇
  免费   3篇
电工技术   6篇
综合类   3篇
化学工业   93篇
金属工艺   5篇
机械仪表   7篇
建筑科学   20篇
矿业工程   1篇
能源动力   8篇
轻工业   77篇
水利工程   7篇
无线电   35篇
一般工业技术   52篇
冶金工业   2860篇
原子能技术   2篇
自动化技术   89篇
  2021年   4篇
  2020年   5篇
  2019年   8篇
  2018年   7篇
  2017年   11篇
  2016年   7篇
  2015年   5篇
  2014年   10篇
  2013年   20篇
  2012年   16篇
  2011年   25篇
  2010年   10篇
  2009年   21篇
  2008年   14篇
  2007年   18篇
  2006年   22篇
  2005年   13篇
  2004年   13篇
  2003年   19篇
  2002年   9篇
  2001年   12篇
  2000年   8篇
  1999年   94篇
  1998年   840篇
  1997年   519篇
  1996年   313篇
  1995年   211篇
  1994年   162篇
  1993年   179篇
  1992年   32篇
  1991年   60篇
  1990年   46篇
  1989年   64篇
  1988年   50篇
  1987年   37篇
  1986年   37篇
  1985年   35篇
  1984年   4篇
  1983年   10篇
  1982年   22篇
  1981年   16篇
  1980年   22篇
  1979年   3篇
  1978年   10篇
  1977年   76篇
  1976年   101篇
  1975年   10篇
  1974年   3篇
  1973年   6篇
  1970年   3篇
排序方式: 共有3265条查询结果,搜索用时 359 毫秒
991.
In the general population, endoscopic retrograde cholangiopancreatography (ERCP) with endoscopic sphincterotomy is preferable to surgery as therapy for gallstone pancreatitis and acute cholangitis. It is particularly attractive to perform therapeutic. ERCP for symptomatic choledocholithiasis after recent myocardial infarction because of the increased risk of the alternative therapy of cholecystectomy and choledochal exploration. However, after myocardial infarction, patients might theoretically be particularly susceptible to the cardiopulmonary risks of ERCP. The safety of therapeutic ERCP after myocardial infarction is unknown, with only one previously reported case. In a review of 11,367 patients with acute myocardial infarction at four hospitals, four patients (0.04%) underwent therapeutic ERCP after recent myocardial infarction, for indications of recent biliary pancreatitis in three of the patients and recent cholangitis in all four. Cholangitis occurred before, simultaneous with, or after myocardial infarction in the four cases. Initially, the cholangitis was managed medically in three patients. The fourth patient underwent cholecystostomy with local anesthesia. ERCP was performed at 15, 25, 30, or 56 days after myocardial infarction. Endoscopic cholangiography revealed multiple choledocholithiasis in all cases. The calculi were successfully extracted by endoscopic papillotomy and by sweeping the choledochus with a balloon-tipped catheter or basket in all cases. During ERCP, the vital signs remained stable; no cardiac arrhythmias or cardiovascular complications occurred. However, one patient developed mild pancreatitis after ERCP, which rapidly resolved with medical therapy. The four patients rapidly improved after ERCP, with normalization of serum levels of routine biochemical parameters of liver function. These four cases and the one prior case report demonstrate that therapeutic ERCP is not absolutely contraindicated after myocardial infarction and suggest that therapeutic ERCP is preferable to surgery for symptomatic choledocholithiasis after myocardial infarction because of the increased mortality of surgery after myocardial infarction.  相似文献   
992.
993.
994.
995.
996.
Alternative hypotheses in higher-level marsupial systematics have different implications for marsupial origins, character evolution, and biogeography. Resolving the position of the South American monito del monte (Order Microbiotheria) is of particular importance in that alternate hypotheses posit sister-group relationships between microbiotheres and taxa with disparate temporal and geographic distributions: pediomyids; didelphids; dasyuromorphians; diprotodontians; all other australidelphians; and all other marsupials. Among Australasian marsupials, the placement of bandicoots is critical; competing views associate bandicoots with particular Australasian taxa (diprotodontians, dasyuromorphians) or outside of a clade that includes all other Australasian forms and microbiotheres. Affinities of the marsupial mole are also unclear. The mole is placed in its own order (Notoryctemorphia) and sister-group relationships have been postulated between it and each of the other Australasian orders. We investigated relationships among marsupial orders by using a data set that included mitochondrial and nuclear genes. Phylogenetic analyses provide support for the association of microbiotheres with Australasian marsupials and an association of the marsupial mole with dasyuromorphs. Statistical tests reject the association of diprotodontians and bandicoots together as well as the monophyly of Australasian marsupials. The origin of the paraphyletic Australasian marsupial fauna may be accounted for by (i) multiple entries of australidelphians into Australia or (ii) bidirectional dispersal of australidelphians between Antarctica and Australia.  相似文献   
997.
998.
BACKGROUND: Efforts to implement continuous quality improvement (CQI) principles in ambulatory or primary care settings still lag behind efforts in the hospital setting. Many physicians view the concept of CQI with unconcealed skepticism; the process of ambulatory care is very different from that of hospital-based care; and the data necessary to guide CQI efforts are often either missing or inaccurate in the outpatient setting. Since fall 1995, the Department of Family Medicine (DFM) at the University of Michigan (Ann Arbor), including approximately 35 faculty members at seven family practice sites, has been engaged in CQI projects. PLANNING AND IMPLEMENTATION: The CQI committee had a six-month deadline to lay out a plan for educating all faculty and staff in the importance of the CQI approach to problems; design methods for all faculty and staff to buy in to the concepts; and develop a plan to address basic clinical CQI activities, administrative systems change and work environment improvement, and larger ad hoc projects in clinical care, educational programs, and research programs. IMPLEMENTATION: CQI activities were incorporated into the routine monthly business agendas at each clinical site, each of which had a functioning local committee and had begun development of at least one CQI project. PROJECTING INTO THE FUTURE AND CONCLUSIONS: Cost cutting has further moved CQI from the sideline to center stage in the DFM's activities. An effective CQI program can be a major asset in the current competitive health care market, but designing and implementing an outpatient CQI program is a difficult and complex process. Three major problems--the ongoing resistance to change, the slow pace of adding CQI projects to already overburdened work schedules, and the need to conduct the program with ever-decreasing resources available-persist.  相似文献   
999.
1000.
We investigated the effects of the drug 14-keto-stypodiol diacetate (SDA) extracted from the seaweed product Stypopodium flabelliforme, in inhibiting the cell growth and tumor invasive behavior of DU-145 human prostate cells. In addition, the molecular action of the drug on microtubule assembly was analyzed. The effects of this diterpenoid drug in cell proliferation of DU-145 tumor cells in culture revealed that SDA at concentrations of 5 microM decreased cell growth by 14%, while at 45 microM a 61% decrease was found, as compared with control cells incubated with the solvent but in the absence of the drug. To study their effects on the cell cycle, DU-145 cells were incubated with increasing concentrations of SDA and the distribution of cell-cycle stages was analyzed by flow cytometry. Interestingly, the data showed that 14-keto-stypodiol diacetate dramatically increased the proportion of cells in the G2/M phases, and decreased the number of cells at the S phase of mitosis, as compared with appropriate controls. Studies on their action on the in vitro assembly of microtubules using purified brain tubulin, showed that SDA delayed the lag period associated to nucleation events during assembly, and decreased significantly the extent of polymerization. The studies suggest that this novel derivative from a marine natural product induces mitotic arrest of tumor cells, an effect that could be associated to alterations in the normal microtubule assembly process. On the other hand, a salient feature of this compound is that it affected protease secretion and the in vitro invasive capacity, both properties of cells from metastases. The secretion of plasminogen activator (u-PA) and the capacity of DU-145 cells to migrate through a Matrigel-coated membrane were significantly inhibited in the presence of micromolar concentrations of SDA. These results provide new keys to analyze the functional relationships between protease secretion, invasive behavior of tumor cells and the microtubule network.  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