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   2559篇
  免费   88篇
  国内免费   3篇
电工技术   185篇
综合类   5篇
化学工业   587篇
金属工艺   88篇
机械仪表   48篇
建筑科学   44篇
矿业工程   1篇
能源动力   108篇
轻工业   202篇
水利工程   5篇
石油天然气   9篇
无线电   213篇
一般工业技术   488篇
冶金工业   337篇
原子能技术   68篇
自动化技术   262篇
  2023年   11篇
  2022年   20篇
  2021年   54篇
  2020年   21篇
  2019年   44篇
  2018年   56篇
  2017年   42篇
  2016年   71篇
  2015年   48篇
  2014年   61篇
  2013年   123篇
  2012年   123篇
  2011年   137篇
  2010年   112篇
  2009年   118篇
  2008年   121篇
  2007年   104篇
  2006年   81篇
  2005年   88篇
  2004年   86篇
  2003年   77篇
  2002年   53篇
  2001年   61篇
  2000年   49篇
  1999年   68篇
  1998年   141篇
  1997年   103篇
  1996年   56篇
  1995年   58篇
  1994年   45篇
  1993年   41篇
  1992年   30篇
  1991年   39篇
  1990年   19篇
  1989年   34篇
  1988年   20篇
  1987年   15篇
  1986年   20篇
  1985年   17篇
  1984年   22篇
  1983年   22篇
  1982年   21篇
  1981年   13篇
  1980年   23篇
  1979年   13篇
  1978年   10篇
  1977年   9篇
  1976年   15篇
  1975年   9篇
  1974年   6篇
排序方式: 共有2650条查询结果,搜索用时 820 毫秒
1.
2.
Some reports demonstrated successful genome editing in pigs by one-step zygote microinjection of mRNA of CRISPR/Cas9-related components. Given the relatively long gestation periods and the high cost of housing, the establishment of a single blastocyst-based assay for rapid optimization of the above system is required. As a proof-of-concept, we attempted to disrupt a gene (GGTA1) encoding the α-1,3-galactosyltransferase that synthesizes the α-Gal epitope using parthenogenetically activated porcine oocytes. The lack of α-Gal epitope expression can be monitored by staining with fluorescently labeled isolectin BS-I-B4 (IB4), which binds specifically to the α-Gal epitope. When oocytes were injected with guide RNA specific to GGTA1 together with enhanced green fluorescent protein (EGFP) and human Cas9 mRNAs, 65% (24/37) of the developing blastocysts exhibited green fluorescence, although almost all (96%, 23/24) showed a mosaic fluorescent pattern. Staining with IB4 revealed that the green fluorescent area often had a reduced binding activity to IB4. Of the 16 samples tested, six (five fluorescent and one non-fluorescent blastocysts) had indel mutations, suggesting a correlation between EGFP expression and mutation induction. Furthermore, it is suggested that zygote microinjection of mRNAs might lead to the production of piglets with cells harboring various mutation types.  相似文献   
3.
Although hydrogen refueling stations (HRSs) are becoming widespread across Japan and are essential for the operation of fuel cell vehicles, they present potential hazards. A large number of accidents such as explosions or fires have been reported, rendering it necessary to conduct a number of qualitative and quantitative risk assessments for HRSs. Current safety codes and technical standards related to Japanese HRSs have been established based on the results of a qualitative risk assessment and quantitative effectiveness validation of safety measures over ten years ago. In the last decade, there has been much development in the technologies of the components or facilities used in domestic HRSs and much operational experience as well as knowledge to use hydrogen in HRSs safely have been gained through years of commercial operation. The purpose of the present study is to conduct a quantitative risk assessment (QRA) of the latest HRS model representing Japanese HRSs with the most current information and to identify the most significant scenarios that pose the greatest risks to the physical surroundings in the HRS model. The results of the QRA show that the risk contours of 10?3 and 10?4 per year were confined within the HRS boundaries, whereas the risk contours of 10?5 and 10?6 per year are still present outside the HRS. Comparing the breakdown of the individual risks (IRs) at the risk ranking points, we conclude that the risk of jet fire demonstrates the highest contribution to the risks at all of the risk ranking points and outside the station. To reduce these risks and confine the risk contour of 10?6 per year within the HRS boundaries, it is necessary to consider risk mitigation measures for jet fires.  相似文献   
4.
In 1992, 1531 women aging 25-45 years from 5 urban and rural regions were interviewed about infertility and subfecundity within the German part of a study by the European community. 1248 of them had a positive reproductive history with 3018 pregnancies. 400 (= 13.25%) occurred during contraception. This affected 296 women (= 19.6% of all women). Smoking seems to have a promotion effect. The risk of ectopic pregnancies seems to be higher in contraceptive users. The highest fetal loss was found in women using an IUD. There were no differences in the course and outcome of pregnancy between users and nonusers of contraceptives. About 40% of the women in the corresponding group reported an irregular application of the contraceptive technique.  相似文献   
5.
6.
Aluminum nitride ceramics were prepared by sintering with 0–4.8 mass% of Ca3Al2O6 (C3A) as a sintering additive. The transmittance in the range of 260–550 nm increased with increasing amount of C3A. The cathodoluminescence intensity attributed to oxygen-induced defects decreased with increasing amount of C3A. From the results, the increase of the transmittance in the range of 260–550 nm was considered to be related to the decrease of the oxygen-induced defect density.  相似文献   
7.
The purpose of this study is to determine whether left ventricular dysfunction following coronary artery spasm by 123I-BMIPP myocardial imaging. To reveal the clinical efficacy of 123I-BMIPP SPECT, 20 patients with vasospastic angina were studied using resting, 3-hour delayed image with 123I-BMIPP and exercise, 3-hour delayed image with 201Tl SPECT. 123I-BMIPP uptake was decreased compared to 201Tl (discordant) in 12 patients (60%) and in 49/100 myocardial segments (49%). The extent and severity score in resting image with 123I-BMIPP were significantly larger than that in delayed image with 201Tl (p < 0.01). In 123I-BMIPP SPECT, the severity score in the latest ischemia were significantly larger than that in others. The incidence of a complete agreement of decreased 123I-BMIPP uptake and coronary artery spasm was significantly higher (75%) than that in 201Tl (28%, p < 0.01). Furthermore, compared to 201Tl uptake, decreased 123I-BMIPP uptake much more corresponded to reduced wall motion in 9 of patients with mismatching. The severity of regional wall motion abnormality was significantly correlated with severity score of 123I-BMIPP. Late redistribution in delayed image with 123I-BMIPP was seen in 6 patients. The regional washout rate and the severity of regional wall motion abnormality in 6 patients was significantly lower than that in others (p < 0.05). Thus, metabolic abnormality assessed by 123I-BMIPP is well associated with left ventricular asynergy and spastic region in patients with vasospastic angina. In conclusion, 123I-BMIPP SPECT may sensitively delineate the impaired myocardium following coronary artery spasm, and it is very useful in diagnosing and estimating the severity of vasospastic angina.  相似文献   
8.
Adenovirus mediated transfer of growth-inhibiting molecules, such as p53 shows promise as an effective method of suppressing the growth of cancer cells. As the basis for in vivo studies, we examined transfection efficiency using 15 human lung cancer cell lines that differ in their endogenous p53 status. When infected with an adenovirus expressing bacterial beta-galactosidase, the different cell lines showed different levels of beta-galactosidase activity. We found a correlation between the level of integrin alpha v beta 5, which is thought to be an adherence receptor for adenoviruses, and the expression level of the transferred gene, suggesting that gene expression is largely dependent on the infection efficiency. Growth inhibition was induced in all cell lines tested following infection with an adenovirus containing p53, regardless of the genetic status of their endogenous p53 provided a sufficient amount of p53 protein was expressed. Our results (1) confirm that the examination of the susceptibility of target cancer cells to an adenovirus is important when considering performing adenovirus-mediated gene transfer and for evaluating its therapeutic effects; and (2) suggest that the quantification of integrin alpha v beta 5 may be a good way of predicting the susceptibility of cells to adenoviral vectors.  相似文献   
9.
10.
A p-MOSFET structure with solid-phase diffused drain (SPDD) is proposed for future 0.1-μm and sub-0.1-μm devices. Highly doped ultrashallow p+ source and drain junctions have been obtained by solid-phase diffusion from a highly doped borosilicate glass (BSG) sidewall. The resulting shallow, high-concentration drain profile significantly improves short channel effects without increasing parasitic resistance. At the same time, an in situ highly-boron-doped LPCVD polysilicon gate is introduced to prevent the transconductance degradation which arises in ultrasmall p-MOSFETs with lower process temperature as a result of depletion formation in the p+-polysilicon gate. Excellent electrical characteristics and good hot-carrier reliability are achieved  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