首页 | 官方网站   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   127657篇
  免费   10450篇
  国内免费   5260篇
工业技术   143367篇
  2024年   586篇
  2023年   2231篇
  2022年   3855篇
  2021年   5287篇
  2020年   4045篇
  2019年   3260篇
  2018年   3812篇
  2017年   4206篇
  2016年   3557篇
  2015年   4835篇
  2014年   6185篇
  2013年   7352篇
  2012年   8142篇
  2011年   8769篇
  2010年   7565篇
  2009年   7066篇
  2008年   6990篇
  2007年   6584篇
  2006年   6813篇
  2005年   5996篇
  2004年   3983篇
  2003年   3416篇
  2002年   3192篇
  2001年   2810篇
  2000年   3075篇
  1999年   3608篇
  1998年   2913篇
  1997年   2347篇
  1996年   2369篇
  1995年   1938篇
  1994年   1582篇
  1993年   1112篇
  1992年   923篇
  1991年   716篇
  1990年   520篇
  1989年   431篇
  1988年   351篇
  1987年   235篇
  1986年   170篇
  1985年   123篇
  1984年   88篇
  1983年   64篇
  1982年   62篇
  1981年   55篇
  1980年   45篇
  1979年   18篇
  1978年   14篇
  1977年   11篇
  1976年   8篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.  相似文献   
22.
Fastmet工艺评述   总被引:5,自引:0,他引:5  
介绍了Fastmet工艺及发展状况,并对工艺特点和指标进行了分析。使用冷固结含碳球团和转底炉使该工艺可直接采用粉矿和提高生产效率,但因硫含量高、铁品位低而产品质量较差。不过投资和生产成本与传统工艺比较却占有较大优势。  相似文献   
23.
This study addresses the influence the 7-substituent on the cytotoxicity of pyrrolo[1,2-alpha]-benzimidazole quinones possessing a 6-aziridinyl group (PBIs) and a 6-acetamido group (APBIs). Reduction of a PBI to the aziridinyl hydroquinone results in both nucleophile trapping (alkylation) and 1,5-sigmatropic shift reactions. The latter process is essentially an internal redox reaction wherein the hydroquinone causes reductive opening of the aziridinyl ring. The 7-substituent controls the fate of the aziridinyl ring by means of steric and electronic effects. An electron-rich 7-substituent favors the 1,5-sigmatropic shift reaction. If the 7-substituent distorts the 6-aziridinyl group from the conformation required for the 1,5-sigmatropic shift, then nucleophile trapping occurs. The 7-methyl substituent results in significant nucleophilic trapping, and the 7-unsubstituted and 7-methoxy substituents favor the 1,5-sigmatropic reaction. Thus, the 7-methyl PBIs show the most cytotoxicity of the analogues studied. The APBIs are cytotoxic only as quinones, and reduction to the hydroquinone results in loss of activity. Consistent with this observation, the change from 7-methyl to the more electron-rich 7-methoxy results in a substantial loss of APBI cytotoxicity as well as decreased topoisomerase II inhibition. The mechanism of inhibition is thought to involve the interacalation of only electron deficient APBIs into DNA.  相似文献   
24.
The magnetization of a melt-texture growth (MTG) HTSC ring has been studied. It is shown that the magnetic field inside the ring is larger than the external field under a certain range of external magnetic fields. We have also investigated the magnetic field dependence of the response of a detective coil near a rotating superconducting ring. The responses of the MTG sample are different for different cooling methods.  相似文献   
25.
Modeling and CW operation of a quasi-three-level 946 nm Nd: YAG laser   总被引:18,自引:0,他引:18  
A model is developed for an end-pumped quasi-three-level laser with population in the lower laser level at equilibrium such as for transitions to the manifolds4I9/2in Nd3+,4I15/2in Er3+,5I8in Ho3+and3H6in Tm3+. It is shown that the effect of residual lower laser level population on laser operation can be treated as a saturable loss. Room temperature operation on the4F3/2-4I9/2transition in Nd:YAG under CW dye laser pumping has been demonstrated with a threshold as low as 11.5 mW incident power and a slope efficiency of 7 percent with 0.3 percent output coupling. Performance is limited by the low output coupling and diffraction loss.  相似文献   
26.
根据托海拱坝5号坝段、7号坝段例垂线实测资料分析,说明了新疆寒冷地区坝体采取聚胺脂喷涂施工措施后对坝体变形的影响,以及右坝肩渗漏对右坝肩岩体的影响,分析结果为托海水电站通过国家电力公司大坝安全监察中心大坝安全首次定检提供了科学依据。  相似文献   
27.
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly.  相似文献   
28.
深穿透复合射孔技术在中原油田的应用   总被引:1,自引:0,他引:1  
深穿透复合射孔是一项把射孔与高能气体压裂两种技术有机地结合在一起的综合改造油气层的新技术。重点对它的技术原理,包括设计原理、枪身内火药燃烧气体对射孔孔眼的冲刷作用原理、火药燃烧气体射流的高能气体压裂作用原理等进行了研究与探讨,同时对它的施工工艺、现场应用等方面进行了阐述,经中原油田189口井现场应用证明,其工艺简便,成本低廉,可实现多层跨隔层使用,处理后增产效果显著,投入产出比高,可代替传统的聚能射孔技术,具有广阔的推广和应用价值。  相似文献   
29.
虚拟仪器(VI)将计算机采集测试分析引入到电子测量领域,用数字化和软件技术极大地提高了测量的灵活性。而VI远程测控系统是网络技术、通信技术一计算机虚拟技术结合的产物。远程控制技术能够使操作突破地域的限制,已在网络环境下PⅢ工控机上实现。  相似文献   
30.
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-23

京公网安备 11010802026262号