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   45316篇
  免费   1120篇
  国内免费   178篇
电工技术   561篇
综合类   633篇
化学工业   5116篇
金属工艺   630篇
机械仪表   882篇
建筑科学   952篇
矿业工程   402篇
能源动力   454篇
轻工业   2314篇
水利工程   662篇
石油天然气   52篇
武器工业   4篇
无线电   2051篇
一般工业技术   3922篇
冶金工业   21548篇
原子能技术   193篇
自动化技术   6238篇
  2024年   57篇
  2023年   204篇
  2022年   128篇
  2021年   146篇
  2020年   53篇
  2019年   77篇
  2018年   544篇
  2017年   766篇
  2016年   1162篇
  2015年   859篇
  2014年   516篇
  2013年   597篇
  2012年   2268篇
  2011年   2602篇
  2010年   791篇
  2009年   879篇
  2008年   724篇
  2007年   828篇
  2006年   649篇
  2005年   3518篇
  2004年   2716篇
  2003年   2158篇
  2002年   916篇
  2001年   752篇
  2000年   305篇
  1999年   639篇
  1998年   6206篇
  1997年   3831篇
  1996年   2542篇
  1995年   1473篇
  1994年   1090篇
  1993年   1128篇
  1992年   258篇
  1991年   317篇
  1990年   313篇
  1989年   282篇
  1988年   299篇
  1987年   223篇
  1986年   203篇
  1985年   184篇
  1984年   72篇
  1983年   90篇
  1982年   135篇
  1981年   184篇
  1980年   197篇
  1979年   70篇
  1978年   102篇
  1977年   619篇
  1976年   1326篇
  1975年   101篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
BACKGROUND: Disturbed fibrinolytic function may influence the progression of coronary atherosclerosis and contribute to thrombotic cardiovascular (CV) events. METHODS AND RESULTS: In the Angina Prognosis Study in Stockholm (APSIS), patients with stable angina pectoris were studied prospectively during double-blind treatment with metoprolol or verapamil. Various measures of fibrinolytic function were studied in 631 (of 809) patients. During a median follow-up time of 3.2 years (2132 patient-years), 32 patients suffered a CV death, 21 had a nonfatal myocardial infarction (MI), and 77 underwent revascularization. Plasma levels of tissue plasminogen activator (TPA) activity and antigen (ag), plasminogen activator inhibitor (PAI-1) activity at test, and TPA responses to exercise were determined at baseline and after 1 month's treatment and were related to subsequent fatal and nonfatal CV events. Univariate Cox regression analysis revealed that elevated levels of TPA-ag at rest (P < .05), high PAI-1 activity (P < .05), and low TPA-ag responses to exercise (P < .05) were associated with increased risk of subsequent CV death. After adjustment for baseline risk factors, TPA-ag independently predicted CV death or MI. In addition, PAI-1 activity independently predicted CV death or MI in male patients. Verapamil treatment was associated with a 10% decrease of TPA-ag levels and metoprolol treatment with a 2% increase (P < .001 for treatment difference). CONCLUSIONS: Plasma TPA-ag levels at rest, and among male patients PAI-1 activity as well, independently predict subsequent CV death or MI in patients with stable angina pectoris.  相似文献   
83.
A theoretical model is presented by which a true expression of pregnancy rate resulting from stimulated cycles can be calculated. This includes the transfer of both fresh and cryopreserved embryos. It is concluded that the total reproductive potential of a single cycle of stimulation can only be evaluated by including pregnancies arising from all fresh and frozen embryo transfers resulting from that cycle.  相似文献   
84.
85.
The tibial diaphysis osteotomy with limited separation of periosteum on the ends of the fragments with subsequent local infection by Staphylococcus aureus culture was conducted. In 90% of observations chronic inflammation was revealed in affected bones while morphological investigation conduction. An acute traumatic disorders of intraosseous blood circulation (the bone infarction) and local staphylococcal infection play the main role in the traumatic osteomyelitis pathogenesis.  相似文献   
86.
87.
A comparative pharmacokinetic study has been performed in 19 healthy male volunteers in a single-dose, randomized, two way cross-over design with two preparations of gemfibrozil (CAS 25812-30-0) capsules each of them containing 300 mg active ingredient. The test preparation was Innogem 300 mg capsule. The plasma concentration of gemfibrozil was determined by a validated HPLC-UV analytical method. The statistical comparison of individual pharmacokinetic parameters (AUC0-16, AUC0-oc Cmax, tmax) of the two capsule preparations was performed by three-way analysis of variance (ANOVA), Wilcoxon's, Westlake's, Schuirmann's and Hanck-Anderson's method as well as by the calculation of confidence intervals on the ratio of test/reference. The relative bioavailability of the test preparation with respect to the reference preparation in terms of the AUC0-oc was 104.06 +/- 21.61%. No statistically significant difference was found between the pharmacokinetic parameters, calculated from plasma concentration-time curves, indicating that the two preparations were bioequivalent.  相似文献   
88.
Tissue and organ transplantation is a very complex interdisciplinary treatment, particularly in regard to unpaired organs, and it carries numerous risks for all participants in such an action. For the purpose of minimizing the risks to the allowed level and the preservation the humanitarian goals in medicine when performing the transplantation, professional and scientific doctrines and the respect of ethical and legal principles should be strictly observed. The paper presents the basic approaches in the estimation of justification, usefulness and certain forms of responsibility in the process of transplantation. Ethical and legal postulates which support transplantation to prevent deviation, deprivation or delinquency have also been reviewed.  相似文献   
89.
90.
OBJECTIVE: The object of the present study was to identify metabolic differences between low-grade astrocytomas and oligodendrogliomas and to improve their diagnosis and noninvasive assessment, because both types of tumors look very similar from the point of view of clinical and radiological data (as assessed by computed tomography and magnetic resonance imaging). METHODS: Before any aggressive treatment, 22 patients with primary low-grade gliomas (astrocytomas in 12 patients and oligodendrogliomas in 10) were investigated with positron emission tomography for both glucose metabolism (18F-fluorodeoxyglucose) and amino acid uptake (11C-L-methylmethionine). An original software that allows a full metabolic analysis of the tumor region of interest (defined from the T1-weighted magnetic resonance image) and compares tumor tissue uptake tracer concentrations with average healthy tissue values has been implemented for data processing. Heterogeneity of each individual tumor has been taken into account and was expressed in histograms, which provided data about the mean and also extreme and intermediate values of tracer concentrations and the way these values are distributed among the full tumor mass. RESULTS: It has been shown that both tumor types exhibit a glucose hypometabolism (slightly more pronounced with astrocytomas), whereas they strongly differ in methionine uptake, which is high in all oligodendrogliomas and either decreased, normal, or moderately increased in astrocytomas. This latter metabolic difference between both tumor populations may be partially explained by their different cell densities. CONCLUSION: This study suggests that despite similar radiological and clinical presentations, these two kinds of low-grade gliomas are metabolically different and could therefore have specific responses to different therapies. Moreover, their in vivo metabolic follow-up with positron emission tomography should rely on different parameters, depending on their histological type; methionine uptake may be more relevant than glucose metabolism in the follow-up of oligodendrogliomas.  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