全文获取类型
收费全文 | 440566篇 |
免费 | 5547篇 |
国内免费 | 1537篇 |
专业分类
电工技术 | 8061篇 |
综合类 | 943篇 |
化学工业 | 63896篇 |
金属工艺 | 16944篇 |
机械仪表 | 14308篇 |
建筑科学 | 9141篇 |
矿业工程 | 2539篇 |
能源动力 | 11894篇 |
轻工业 | 30236篇 |
水利工程 | 4787篇 |
石油天然气 | 7960篇 |
武器工业 | 21篇 |
无线电 | 50907篇 |
一般工业技术 | 85951篇 |
冶金工业 | 92311篇 |
原子能技术 | 9349篇 |
自动化技术 | 38402篇 |
出版年
2022年 | 2658篇 |
2021年 | 3975篇 |
2020年 | 2950篇 |
2019年 | 3843篇 |
2018年 | 6912篇 |
2017年 | 7101篇 |
2016年 | 7897篇 |
2015年 | 5053篇 |
2014年 | 7520篇 |
2013年 | 20380篇 |
2012年 | 13320篇 |
2011年 | 17466篇 |
2010年 | 12742篇 |
2009年 | 14395篇 |
2008年 | 14592篇 |
2007年 | 14360篇 |
2006年 | 12921篇 |
2005年 | 14216篇 |
2004年 | 12910篇 |
2003年 | 12346篇 |
2002年 | 10625篇 |
2001年 | 10430篇 |
2000年 | 9394篇 |
1999年 | 10001篇 |
1998年 | 29036篇 |
1997年 | 19654篇 |
1996年 | 14820篇 |
1995年 | 10677篇 |
1994年 | 9222篇 |
1993年 | 9269篇 |
1992年 | 6258篇 |
1991年 | 5938篇 |
1990年 | 5927篇 |
1989年 | 5547篇 |
1988年 | 5286篇 |
1987年 | 4611篇 |
1986年 | 4461篇 |
1985年 | 4962篇 |
1984年 | 4478篇 |
1983年 | 4065篇 |
1982年 | 3760篇 |
1981年 | 3894篇 |
1980年 | 3591篇 |
1979年 | 3379篇 |
1978年 | 3422篇 |
1977年 | 4302篇 |
1976年 | 6046篇 |
1975年 | 2939篇 |
1974年 | 2697篇 |
1973年 | 2773篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
BACKGROUND: Recently, investigators have reported the use of endoscopic myotomy in the treatment of esophageal achalasia. As with the open operation, considerable disagreement exists regarding the appropriate length of the myotomy and the need for a concomitant antireflux procedure. METHODS: Patients presenting with symptomatic achalasia between 1993 and 1997 were included in this prospective study. Preoperative studies included barium upper gastrointestinal study, endoscopy, and esophageal manometry. Laparoscopic myotomy was completed in all 20 patients; 18 had concomitant Toupet fundoplication. RESULTS: Operative times ranged from 95 to 345 minutes (mean 216). Blood loss ranged from 50 to 300 cc (mean 100 cc). There were 7 minor complications (5 mucosal injuries repaired laparoscopically, 1 bile leak and 1 splenic capsular tear). Nine patients began a liquid diet on the first day postoperatively; 19 were tolerating liquids by postoperative day 3. Hospital stay ranged from 2 to 20 days (mean 5). Eighteen patients had complete relief of dysphagia, with less than one reflux episode per month. One individual continues to have mild persistent solid food dysphagia. Another patient initially did well but subsequently developed mild recurrent dysphagia and reflux. One patient required laparoscopic take-down of the wrap because of recurrent dysphagia and now has no problems swallowing, but does complain of mild reflux. Two other patients also have mild reflux, 1 of whom did not undergo fundoplication. CONCLUSIONS: Laparoscopic Heller myotomy can be performed safely with excellent results in patients with achalasia. Adding a partial fundoplication appears to help control postoperative symptoms of reflux. This procedure should be considered the procedure of choice in patients with symptomatic esophageal achalasia. 相似文献
992.
I Nishijima T Nakahata S Watanabe K Tsuji I Tanaka Y Hirabayashi T Inoue K Arai 《Canadian Metallurgical Quarterly》1997,90(3):1031-1038
Using a clonal assay of bone marrow (BM) cells from transgenic mice (Tg-mice) expressing the human granulocyte-macrophage colony-stimulating factor receptor (hGM-CSFR), we found in earlier studies that hGM-CSF alone supported the development not only of granulocyte-macrophage colonies, but also of erythrocytes, megakaryocytes, mast cells, blast cells, and mixed hematopoietic colonies. In this report, we evaluated the in vivo effects of hGM-CSF on hematopoietic and lymphopoietic responses in the hGM-CSFR Tg-mice. Administration of this factor to Tg-mice resulted in dose-dependent increases in numbers of reticulocytes and white blood cells (WBCs) in the peripheral blood. Morphological analysis of WBCs showed that the numbers of all types of the cell, including neutrophils, eosinophils, monocytes, and lymphocytes increased; the most remarkable being in lymphocytes that contained a number of large granular lymphocytes (LGLs) in addition to mature T and B cells. However, total cellularity of the BM of the Tg-mice decreased in a dose-dependent manner when hGM-CSF was injected. In sharp contrast to the BM, spleens of the Tg-mice were grossly enlarged. Although all types of blood cells and hematopoietic progenitors increased in the spleen, erythroid cells and their progenitors showed the most significant increase. Increased numbers of megakaryocytes and LGLs were also observed in spleen and liver of the treated Tg-mice. Flow cytometric analysis showed that LGLs expanded in Tg-mice expressed Mac-1+ CD3- NK1.1+. The thymus of Tg-mice treated with hGM-CSF exhibited a dose-dependent shrinkage and a remarkable decrease in CD4+ CD8+ cells. Thus, hGM-CSF stimulated not only myelopoiesis but also erythropoiesis and megakaryopoiesis of hGM-CSFR Tg-mice in vivo, in accordance with our reported in vitro findings. In addition, hGM-CSF affected the development of lymphoid cells, including natural killer cells of these Tg-mice. 相似文献
993.
Hemiballism is a rare hyperkinetic disorder which is characterized by irregular vigorous rotatory movements of the limbs of one side of the body. The disabling and exhausting movements with their high risk of severe injuries require an acute drug treatment. However, there are no common guidelines for the treatment of this disorder. Therefore we reviewed the available literature to establish a concept for a rational symptomatic drug treatment. Furthermore, own observations in 6 patients with hemiballism of different origins are reported. 相似文献
994.
995.
B Neppolian H C Choi S Sakthivel Banumathi Arabindoo V Murugesan 《Journal of hazardous materials》2002,89(2-3):303-317
The photocatalytic degradation of three commercial textile dyes with different structure has been investigated using TiO(2) (Degussa P25) photocatalyst in aqueous solution under solar irradiation. Experiments were conducted to optimise various parameters viz. amount of catalyst, concentration of dye, pH and solar light intensity. Degradation of all the dyes were examined by using chemical oxygen demand (COD) method. The degradation efficiency of the three dyes is as follows: Reactive Yellow 17(RY17) > Reactive Red 2(RR2) > Reactive Blue 4 (RB4), respectively. The experimental results indicate that TiO(2) (Degussa P25) is the best catalyst in comparison with other commercial photocatalysts such as, TiO(2) (Merck), ZnO, ZrO(2), WO(3) and CdS. Though the UV irradiation can efficiently degrade the dyes, naturally abundant solar irradiation is also very effective in the mineralisation of dyes. The comparison between thin-film coating and aqueous slurry method reveals that slurry method is more efficient than coating but the problems of leaching and the requirement of separation can be avoided by using coating technique. These observations indicate that all the three dyes could be degraded completely at different time intervals. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams. 相似文献
996.
Storozhuk V. N. Romashchenko V. A. Lepikhin P. P. Zhurakhovskii S. V. 《Strength of Materials》2002,34(3):300-304
Large deflections of pulse-loaded elliptic and round plates made of hardenable elastoplastic materials are investigated analytically using an energy-based approach. Formulas that are convenient for engineering design have been derived. 相似文献
997.
V. B. Baiburin Yu. P. Volkov E. M. Il’in S. V. Semenov 《Technical Physics Letters》2002,28(12):981-982
The surface of a palladium-barium cathode was studied using scanning probe microscopy techniques. Data from the tunneling spectroscopy showed the pattern of the electron work function distribution over a microscopic region on the emitter surface. This pattern is compared to the distribution of various phases in the palladium-barium alloy employed. 相似文献
998.
Tour J.M. Van Zandt W.L. Husband C.P. Husband S.M. Wilson L.S. Franzon P.D. Nackashi D.P. 《Nanotechnology, IEEE Transactions on》2002,1(2):100-109
Molecular electronics seeks to build electrical devices to implement computation - logic and memory - using individual or small collections of molecules. These devices have the potential to reduce device size and fabrication costs, by several orders of magnitude, relative to conventional CMOS. However, the construction of a practical molecular computer will require the molecular switches and their related interconnect technologies to behave as large-scale diverse logic, with input/output wires scaled to molecular dimensions. It is unclear whether it is necessary or even. possible to control the precise regular placement and interconnection of these diminutive molecular systems. This paper describes genetic algorithm-based simulations of molecular device structures in a nanocell where placement and connectivity of the internal molecular switches are not specifically directed and the internal topology is generally disordered. With some simplifying assumptions, these results show that it is possible to use easily fabricated nanocells as logic devices by setting the internal molecular switch states after the topological molecular assembly is complete. Simulated logic devices include an inverter, a NAND gate, an XOR gate and a 1-bit adder. Issues of defect and fault tolerance are addressed. 相似文献
999.
1000.
HBM ESD tests on two types of 0.6 μm DRAM devices showed that internal circuit or output driver failures would occur after the input or I/O pins were ESD stressed negative with respect to Vcc at ground. These failures occurred at lower than expected ESD stress voltages due to power-up circuit interactions that either turned-on unique internal parasitic ESD current paths or disrupted the normal operation of the output pin’s ESD protection circuit. ESD analysis found there exists a set of power-up sensitive circuits and if placed near a Vcc bond pad can result in low voltage ESD failures. 相似文献