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   3397篇
  免费   39篇
  国内免费   3篇
电工技术   37篇
化学工业   442篇
金属工艺   27篇
机械仪表   56篇
建筑科学   101篇
矿业工程   5篇
能源动力   44篇
轻工业   170篇
水利工程   18篇
石油天然气   4篇
无线电   309篇
一般工业技术   333篇
冶金工业   1646篇
原子能技术   20篇
自动化技术   227篇
  2021年   25篇
  2020年   16篇
  2019年   19篇
  2018年   31篇
  2017年   24篇
  2016年   33篇
  2015年   19篇
  2014年   49篇
  2013年   121篇
  2012年   63篇
  2011年   88篇
  2010年   57篇
  2009年   77篇
  2008年   73篇
  2007年   73篇
  2006年   62篇
  2005年   67篇
  2004年   83篇
  2003年   49篇
  2002年   65篇
  2001年   30篇
  2000年   45篇
  1999年   68篇
  1998年   481篇
  1997年   272篇
  1996年   176篇
  1995年   129篇
  1994年   104篇
  1993年   114篇
  1992年   61篇
  1991年   42篇
  1990年   56篇
  1989年   35篇
  1988年   42篇
  1987年   34篇
  1986年   34篇
  1985年   37篇
  1984年   31篇
  1983年   48篇
  1982年   25篇
  1981年   41篇
  1980年   35篇
  1979年   19篇
  1978年   26篇
  1977年   67篇
  1976年   127篇
  1975年   27篇
  1974年   16篇
  1973年   18篇
  1972年   15篇
排序方式: 共有3439条查询结果,搜索用时 31 毫秒
11.
The effects of azadirachtin, salannin, nimbin, and 6-desacetylnimbin on ecdysone 20-monooxygenase (E-20-M) activity were examined in three insect species. Homogenates of wandering stage third instar larvae of Drosophila melanogaster, or abdomens from adult female Aedes aegypti, or fat body or midgut from fifth instar larvae of Manduca sexta were incubated with radiolabeled ecdysone and increasing concentrations (from 1 x 10(-8) to 1 x 10(-3) M) of the four compounds isolated from seed kernels of the neem tree, Azadirachta indica. All four neem tree compounds were found to inhibit, in a dose-dependent fashion, the E-20-M activity in three insect species. The concentration of these compounds required to elicit a 50% inhibition of this steroid hydroxylase activity in the three insect species examined ranged from approximately 2 x 10(-5) to 1 x 10(-3).  相似文献   
12.
Sixty-five patients initially seropositive for IgM anti-phenolic glycolipid-I (PGL-I) antibodies were tested for antibody levels to PGL-I, lipoarabinomannan (LAM), and the 35-kDa protein of Mycobacterium leprae at regular intervals for up to 30 months following the commencement of multidrug therapy (MDT). There was a steady decline in IgM anti-PGL-I and anti-35-kDa antibody levels to a mean of 17% and 14%, respectively, of the starting level at 24 months. The development of type 1 and type 2 reactions or the presence of drug-resistant organisms in a small number of patients had no significant influence on the changes in antibody level. The rate of decline was similar in different disease categories, but a higher proportion of lepromatous patients remained seropositive at the end of 2 years of treatment than borderline tuberculoid patients. By contrast, the mean IgG anti-LAM antibody levels remained stable or increased. Again the occurrence of type 1 or type 2 reactions had no significant effect on antibody level over 2 years. Falls in the IgM anti-PGL-I antibody levels mirrored the falls in the bacterial index in individual patients and provide an additional parameter for monitoring the response to chemotherapy.  相似文献   
13.
The rapid advances in molecular biology have begun to shift many of the bottlenecks in genome research from the laboratory to the data analysis facility. The pace at which this has occurred creates a situation in which software development always has to catch up with the flow of data. Since such large-scale processes were not anticipated, the analysis infrastructure has not been fully established. Furthermore, most systems that have been built were designed by the biologists who collected the data. More recently, computer scientists, mathematicians, and engineers have taken an interest in this problem. This has had a positive effect, since it has created a tight synergy between the informatics and the biology. Several principles affected the design of the system developed at TIGR. Each of the sample preparation, sequencing, and analysis steps had to be managed, scheduled, and tracked. This information had to be made readily available to those who needed it for carrying out their tasks. Different skill levels of the users had to be taken into account. The degree of human intervention at each step had to be evaluated and built into the design. A mixed processing environment of Macintosh and Unix platforms had to be integrated. Most importantly, the system had to save time, reduce error, and ensure uniformity of the analysis and quality of the results. In the authors' experience, the tools they have built work well because of their early decisions as to which systems to use for development. The authors settled on a robust relational database management system (Sybase) and a portable development environment (C, C++)  相似文献   
14.
15.
The charts of all patients with acute cholecystitis undergoing either laparoscopic or minilap cholecystectomy at the Chinle Comprehensive Health Care Facility between October 1, 1991, and August 15, 1993, were retrospectively reviewed. During that period, 54 patients underwent laparoscopic cholecystectomy and 45 patients had minilap procedures. The two groups had similar mean age, sex distribution, temperature, leukocyte count, gallbladder wall thickness, and duration of preoperative symptoms. While laparoscopic cholecystectomy took an average of 16 min longer to perform than minilap cholecystectomy, patients who had laparoscopic cholecystectomy had less blood loss, reduced postoperative narcotic needs, and shorter hospital stays.  相似文献   
16.
Thomson  J. Adams  D. Walker  K. 《Computer》2003,36(12):27-34
Computational and laboratory experiments generate masses of data that must be stored reliably, with minimal effort on each researcher's part, and must be retrievable for decades. The storage environment must also work seamlessly across scientific disciplines and capture all of a file system's features in a semantically-based catalog that provides Boolean, keyword, and tree-based data access. The authors describe a metadata-based archive for scientific data that provides flexible archive storage for very large data sets. The system uses metadata to organize and manage the data without imposing predefined metadata formats on scientists.  相似文献   
17.
BACKGROUND: In spring 1995 pharmacists representing each of the 23 member hospitals in Synernet, a hospital cooperative in Maine, decided to collaborate in developing a multihospital medication use evaluation (MUE) program. The committee set up task forces for adverse drug reaction reporting and prevention, MUE plans, and medication error reporting and prevention, for exploration of opportunities to eliminate duplication of efforts, compare performance, and share best practices. PLANNING THE PROGRAM: The members retained a consulting firm to manage the SynRx medication use program from conceptualization through implementation. Modules--on individual drug dosing, switching from intravenous to oral administration, pharmacists' clinical recommendations, and surgical antibiotic prophylaxis--were designed so that participants could adopt the entire plan as a turnkey procedure by inserting their hospital name in the appropriate blanks, modify it to more closely fit their own organizations, use portions of it for inclusion in their current plans, or not use it at all. The goal was to build in maximum flexibility to accommodate the variations in the participating hospital pharmacies and their respective hospitals. RESULTS: Early program benefits include improvements in medication event reporting, documentation of the measured aspects of medication use, delivery of care processes, and administrative efficiency. LESSONS LEARNED AND CONCLUSIONS: The participants, consultants, and programmers involved in the SynRx program learned firsthand the complexity and magnitude of hospital medication use processes. Yet it is possible to overcome the wide variability in systems among hospitals to create standards that allow for more meaningful comparisons of medication use.  相似文献   
18.
The known effects of commonly used nonsteroidal anti-inflammatory drugs (NSAIDs) on hemostatic parameters have led to concern over their use in the perioperative period. Nabumetone, unlike other NSAIDs, has little effect on collagen-induced platelet aggregation. To evaluate the effect of nabumetone 2000 mg daily on other hemostatic parameters (e.g., bleeding time, prothrombin time, and partial thromboplastin time) in the clinical setting, this double-masked study was conducted in patients with osteoarthritis undergoing arthroscopic knee surgery. After a 1-week placebo washout period, 58 patients were randomized to receive nabumetone and 53 were randomized to receive placebo. They were assessed before surgery (after 1 to 2 weeks of treatment) and again after surgery (after an additional 3 weeks of treatment). The study was designed to have 90% power to show equivalence in bleeding time to within 1.5 minutes, a difference assumed to be of no clinical importance. No meaningful differences were observed between the groups in any of the measured hemostatic parameters. Before surgery, the bleeding time increased by only 0.3 minutes with nabumetone and decreased by 0.2 minutes with placebo. The mean (+/- SD) difference between the groups in change from baseline was 0.5 +/- 0.3 minutes. After surgery, the changes were 0.1 minutes and 0.0 minutes, respectively, and the difference between groups was 0.2 +/- 0.3 minutes. These differences were neither statistically nor clinically significant, and maximum individual increases were similar in each group. Furthermore, there were no reports of abnormal bleeding in the operative knees. The results of this study show that nabumetone had little or no effect on hemostasis and suggest that this drug can be used safely in the perioperative period.  相似文献   
19.
Unequal metabolic responses to trauma by women and men have been suggested, but an explicit investigation demonstrating this conjecture has not been made. The responses of resting energy expenditure (REE) and nitrogen balance for 3 days before and 7 days after skeletal trauma were determined for female and male rats. Food intake and body weight were recorded daily, and 24-h urine samples were collected. Baseline REE and nitrogen balance were obtained for 3 consecutive days before induction of trauma. Then rats were divided into female trauma (n = 8), male trauma (n = 7), female control (n = 8), and male control (n = 7) groups. Trauma was produced by bilateral femoral fracture to anesthetized rats. Control rats were anesthetized without skeletal trauma. Traumatized rats were fed ad libitum for 7 days, and control rats were pair fed with the traumatized rats. The results showed that REE increased and nitrogen balance decreased in traumatized male rats relative to their controls. Traumatized female rats had increased REE and unchanged nitrogen balance compared with their controls. Traumatized female rats had a larger percentage increase in REE on days 5 through 7 than did traumatized male rats. These findings demonstrate a difference between female and male rats in response to trauma. Female rats use more energy and lose less nitrogen after trauma than do male rats. The results suggest that recommendations for increased energy and protein needs after trauma should consider the sex of the subject intended to be fed.  相似文献   
20.
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