全文获取类型
收费全文 | 201978篇 |
免费 | 2691篇 |
国内免费 | 798篇 |
专业分类
电工技术 | 4246篇 |
综合类 | 375篇 |
化学工业 | 27305篇 |
金属工艺 | 7727篇 |
机械仪表 | 5658篇 |
建筑科学 | 4366篇 |
矿业工程 | 874篇 |
能源动力 | 4767篇 |
轻工业 | 14621篇 |
水利工程 | 1780篇 |
石油天然气 | 2991篇 |
武器工业 | 53篇 |
无线电 | 27921篇 |
一般工业技术 | 38022篇 |
冶金工业 | 45927篇 |
原子能技术 | 3608篇 |
自动化技术 | 15226篇 |
出版年
2021年 | 1435篇 |
2020年 | 1038篇 |
2019年 | 1399篇 |
2018年 | 2261篇 |
2017年 | 2248篇 |
2016年 | 2287篇 |
2015年 | 1667篇 |
2014年 | 2792篇 |
2013年 | 8164篇 |
2012年 | 4684篇 |
2011年 | 6385篇 |
2010年 | 5177篇 |
2009年 | 6009篇 |
2008年 | 6413篇 |
2007年 | 6402篇 |
2006年 | 5822篇 |
2005年 | 5451篇 |
2004年 | 5344篇 |
2003年 | 5182篇 |
2002年 | 4987篇 |
2001年 | 5402篇 |
2000年 | 5029篇 |
1999年 | 5565篇 |
1998年 | 15820篇 |
1997年 | 10449篇 |
1996年 | 8031篇 |
1995年 | 5845篇 |
1994年 | 5078篇 |
1993年 | 5081篇 |
1992年 | 3411篇 |
1991年 | 3282篇 |
1990年 | 3236篇 |
1989年 | 3064篇 |
1988年 | 2809篇 |
1987年 | 2253篇 |
1986年 | 2328篇 |
1985年 | 2619篇 |
1984年 | 2337篇 |
1983年 | 2079篇 |
1982年 | 1913篇 |
1981年 | 2049篇 |
1980年 | 1798篇 |
1979年 | 1668篇 |
1978年 | 1669篇 |
1977年 | 2028篇 |
1976年 | 2735篇 |
1975年 | 1427篇 |
1974年 | 1375篇 |
1973年 | 1318篇 |
1972年 | 1127篇 |
排序方式: 共有10000条查询结果,搜索用时 750 毫秒
971.
Force modulation microscopy (FMM) is used to characterize the external surface and internal fracture surface morphologies of three different block copolymer samples. A roll-cast poly(styrene-butadiene-styrene) triblock copolymer film, spin-coated poly(styrene-b-methyl methacrylate) thin films, and an ultrathin poly(styrene-b-hexyl isocyanate) rod-coil block copolymer film were investigated. For each sample, height and elasticity images were obtained for the same areas allowing direct comparison. The elasticity images obtained using force modulation microscopy were independent of surface roughness and found to exhibit better contrast and spatial resolution of the respective block copolymer domains than the height images. The lateral resolution of the elasticity images was sufficient to show microphase separated domains having length scales as small as about 10 nm. The poly(styrene-b-methyl methacrylate) samples demonstrate that FMM can even be successfully used to study block copolymers in which both blocks are glassy under the conditions of measurement. 相似文献
972.
Analysis of composite laminates with transverse cracks 总被引:1,自引:0,他引:1
The analysis of the behaviour of composite laminates with general balanced lay-up sequences and containing distributed transverse cracks is discussed and demonstrated in this paper. It is shown that a constitutive model of damage for composites, which has been successfully used to analyse the effects of uniformly distributed transverse cracks in cross-ply laminates, can be readily extended to the analysis of uniformly distributed transverse cracks in more general symmetric laminates. The further extension of the theory to non-uniformly distributed damage can be achieved by finite element analysis. It is shown that the finite element implementation of the theory is particularly simple since the contribution of the damage to the overall behaviour can be incorporated into the force vectors. 相似文献
973.
974.
When a heterogeneous elastic material is represented by an effective homogeneous elastic solid, average stress and strain fields are used. The meaning of the J-integral in the effective homogeneous solid is investigated. A periodically layered medium is considered. The relation between the J-integrals in the original layered medium and the effective medium is derived. 相似文献
975.
Saito M. Yoshitomi T. Hara H. Ono M. Akasaka Y. Nii H. Matsuda S. Momose H.S. Katsumata Y. Ushiku Y. Iwai H. 《Electron Devices, IEEE Transactions on》1993,40(12):2264-2272
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
976.
C Serveau L Juliano P Bernard T Moreau R Mayer F Gauthier 《Canadian Metallurgical Quarterly》1994,76(2):153-158
A discontinuous borate/formate buffer system is presented for horizontal polyacrylamide gel electrophoresis of DNA fragments. The resolution potential of the system could be altered by changing the total monomer concentration (5-9%T), the concentration of the crosslinker piperazine diacrylamide (2-5%CPDA), as well as the concentration of formate in the gel (40-120 mM), the leading ion of the buffer system. The separation of DNA fragments would be improved by increasing the migration distance from 22 to 28 cm. This discontinuous polyacrylamide gel electrophoresis system proved highly reproducible. 相似文献
977.
In many firms' experience, reusing elements of proven systems designs and software is best done through a companywide program. Reuse means savings in design, testing, manufacturing and support. The author gives the basic information a company needs to get started. The author discusses the context for reuse, planning and strategy involved in a reuse program 相似文献
978.
GB virus C (GBV-C) RNA was detected in five of 18 patients with aplastic anaemia who had received blood transfusions, whereas it was not detected in eight patients who had not received any transfusions. Antibody against hepatitis C virus (anti-HCV) was detected in nine patients in the transfusion group, compared with one of eight who had not received any transfusions. Therefore, the route of transmission of both GBV-C and HCV in these patients appeared to have been multiple blood transfusion. Since all of the GBV-C RNA-positive patients harboured anti-HCV, GBV-C seems to frequently superinfect with HCV. Neither GBV-C nor HCV is likely to have been a causative agent of the anaemia in the cases examined. 相似文献
979.
H Midorikawa A Tsuda K Satoh K Akuzawa T Igari S Hoshino 《Canadian Metallurgical Quarterly》1997,50(13):1104-1107
This report describes a case in which a 68-year-old male underwent two operations simultaneously for left coronary ostial stenosis and gastric cancer. Successfully performed procedures were a single coronary artery grafting with the saphenous vein to the left anterior descending artery, and a subtotal gastrectomy using the Billroth II method. The postoperative course was uneventful and the patient was discharged from the hospital in good condition after 42 days. At present, one-year postoperative, the patient has been visiting the outpatient clinic in healthy condition. 相似文献
980.
Pentacene-based organic thin-film transistors 总被引:7,自引:0,他引:7
Yen-Yi Lin Gundlach D.I. Nelson S.F. Jackson T.N. 《Electron Devices, IEEE Transactions on》1997,44(8):1325-1331
Organic thin-film transistors using the fused-ring polycyclic aromatic hydrocarbon pentacene as the active electronic material have shown mobility as large as 0.7 cm2/V-s and on/off current ratio larger than 108; both values are comparable to hydrogenated amorphous silicon devices. On the other hand, these and most other organic TFT's have an undesirably large subthreshold slope. We show here that the large subthreshold slope typically observed is not an intrinsic property of the organic semiconducting material and that devices with subthreshold slope similar to amorphous silicon devices are possible 相似文献