全文获取类型
收费全文 | 1724638篇 |
免费 | 27408篇 |
国内免费 | 7303篇 |
专业分类
电工技术 | 35833篇 |
综合类 | 6631篇 |
化学工业 | 283767篇 |
金属工艺 | 68143篇 |
机械仪表 | 50299篇 |
建筑科学 | 51009篇 |
矿业工程 | 12136篇 |
能源动力 | 50859篇 |
轻工业 | 138356篇 |
水利工程 | 17633篇 |
石油天然气 | 38620篇 |
武器工业 | 164篇 |
无线电 | 203754篇 |
一般工业技术 | 319471篇 |
冶金工业 | 266777篇 |
原子能技术 | 34928篇 |
自动化技术 | 180969篇 |
出版年
2021年 | 15996篇 |
2020年 | 12332篇 |
2019年 | 15144篇 |
2018年 | 21006篇 |
2017年 | 20820篇 |
2016年 | 24356篇 |
2015年 | 18108篇 |
2014年 | 29277篇 |
2013年 | 89104篇 |
2012年 | 41605篇 |
2011年 | 58749篇 |
2010年 | 48518篇 |
2009年 | 55571篇 |
2008年 | 53391篇 |
2007年 | 51837篇 |
2006年 | 49664篇 |
2005年 | 45900篇 |
2004年 | 46528篇 |
2003年 | 45990篇 |
2002年 | 44173篇 |
2001年 | 41498篇 |
2000年 | 39231篇 |
1999年 | 40085篇 |
1998年 | 76794篇 |
1997年 | 58591篇 |
1996年 | 47986篇 |
1995年 | 38326篇 |
1994年 | 34829篇 |
1993年 | 34736篇 |
1992年 | 27989篇 |
1991年 | 25446篇 |
1990年 | 25651篇 |
1989年 | 24721篇 |
1988年 | 23324篇 |
1987年 | 21377篇 |
1986年 | 20780篇 |
1985年 | 24138篇 |
1984年 | 23295篇 |
1983年 | 21307篇 |
1982年 | 20023篇 |
1981年 | 20246篇 |
1980年 | 18931篇 |
1979年 | 19194篇 |
1978年 | 18438篇 |
1977年 | 19866篇 |
1976年 | 23431篇 |
1975年 | 16534篇 |
1974年 | 15916篇 |
1973年 | 16086篇 |
1972年 | 13524篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
A therapist's theoretical orientation is likely to influence every facet of the therapeutic process. We explore the relationship of therapeutic orientation and self-monitoring style. To test the hypothesis that high self-monitors would be more eclectic than low self-monitors, we surveyed 30 intake therapists at a child guidance center. Results supported the hypothesis; those frequently using more than one orientation had higher self-monitoring scores. Furthermore, self-monitoring correlated negatively with psychoanalytic endorsement, but in a positive direction with behavioral, systems and eclectic endorsements. Results are discussed in terms of training needs of those differing in self-monitoring style. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
994.
ABSTRACT: The objective of this work was to observe the microstructure of feta cheese using confocal scanning laser microscopy. Low fat cheese and cheese containing capsule-producing cultures were made. The protein network was observed using the reflectance mode of the confocal microscope. Fat was stained by Nile red dye diluted with whey. More even distribution of fat with a larger number of smaller globules was observed in cheese made with noncapsule-forming culture compared to that made with the capsule-forming culture. Nonfat cheese had compact structure when made with noncapsule-forming culture which contrasted with the open structure observed in cheese made with the capsule-forming culture 相似文献
995.
This paper proposes a method to reduce the vibration of the three-phase HB-type stepping motor with cogging torque by the feedforward compensation control. The compensation signal to suppress the vibration of the motor frame is obtained by the repetitive controller installing an online Fourier transformer and utilizing an acceleration sensor attached to the motor frame or an acoustic sensor such as a microphone placed close to the frame. The sensor is used only for the acquisition of the feedforward compensation data. The feedforward compensation signal at an arbitrary operating point is derived from the amplitude and phase data of the frequency components and the operating point data. Compensation data obtained by the repetitive controller is applied to the operating point changed by reference frequency and load condition in steady state. The compensation signal for the new operating point will be generated from compensation data utilizing polynomial equation approximation and linear interpolation method. The effectiveness of this proposed method is confirmed by the experimental results. 相似文献
996.
McDonald K.C. Zimmermann R. Kimball J.S. 《Geoscience and Remote Sensing, IEEE Transactions on》2002,40(9):2063-2082
Spatial and temporal variations in vegetation dielectric properties strongly influence the microwave backscatter characteristics of forested landscapes. This paper examines the relationship between xylem tissue dielectric constant, xylem sap flux density, and xylem sap chemical composition as measured in the stems of two Norway Spruce (Picea abies [L.] Karst.) trees in the Fichtelgebirge region of Northern Bavaria, Germany. Dielectric constant and xylem sap flux were monitored continuously from June through October 1995, at several heights along the tree trunks. At the end of the measurement series, each tree was harvested, and its xylem sap extracted and analyzed to determine the concentrations of amino acids and cations. Results show that the sap flux density was correlated with vapor pressure deficit (VPD) at all heights in the stem. In contrast, the xylem tissue dielectric constant is influenced by VPD but can exhibit a significant temporal lag relative to changes in VPD. This lag varies with position along the tree trunk. The temporal variability of the dielectric constant is compared with both trees at several positions along the tree trunks. Results of xylem sap chemical analysis are presented. We show that spatial and temporal variability in the xylem tissue dielectric constant is influenced not only by water content, but by variations in xylem sap chemistry as well. This has important implications for microwave remote sensing of forested landscapes, as useful information may be acquired regarding stand physiology and water relations and where variations in dielectric properties within individual trees and across geographic areas can be significant error sources for forest inventory mapping. 相似文献
997.
998.
MB Heyman JM LaBerge KA Somberg P Rosenthal C Mudge EJ Ring JD Snyder 《Canadian Metallurgical Quarterly》1997,131(6):914-919
The transjugular intrahepatic portosystemic shunt procedure is an accepted treatment for adults with complications of portal hypertension. We performed a retrospective review of all pediatric TIPS placements performed at the University of California, San Francisco between 1990 and 1996. Twelve procedures were attempted in nine children, with a mean age (+/- SD) of 9.4 +/- 3.9 years (range, 5 to 15 years) and a mean weight of 31 +/- 18 kg (range, 16 to 70 kg). The indications for TIPS placement were portal hypertension complicated by chronic variceal hemorrhage not controlled with sclerotherapy (n = 7) and hypersplenism with thrombocytopenia (n = 2). TIPS placement was successfully completed initially in seven of nine (78%) patients. Unfavorable vascular anatomy was the cause of failure in two cases. The seven patients who underwent successful TIPS placement were followed up for an average of 136 days (range, 1 to 800 days); two still have patent shunts, three underwent liver transplantation, one had a splenorenal shunt after stenosis, and one died of underlying liver disease. Variceal bleeding was controlled in four of five patients who successfully underwent TIPS placement. Shunt occlusion occurred in four patients; patency was restored by transjugular shunt revision in three, and a splenorenal shunt was performed in one. 相似文献
999.
MA Nowak AL Lloyd GM Vasquez TA Wiltrout LM Wahl N Bischofberger J Williams A Kinter AS Fauci VM Hirsch JD Lifson 《Canadian Metallurgical Quarterly》1997,71(10):7518-7525
Mathematical modeling of viral replication dynamics, based on sequential measurements of levels of virion-associated RNA in plasma during antiretroviral treatment, has led to fundamental new insights into human immunodeficiency virus type 1 pathogenesis. We took advantage of the simian immunodeficiency virus (SIV)-infected macaque model to perform detailed measurements and mathematical modeling during primary infection and during treatment of established infection with the antiretroviral drug (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA). The calculated clearance half-life for productively infected cells during resolution of the peak viremia of primary infection was on the order of 1 day, with slightly shorter clearance half-lives calculated during PMPA treatment. Viral reproduction rates upon discontinuation of PMPA treatment after 2 weeks were approximately twofold greater than those obtained just prior to initiation of treatment in the same animals, likely reflecting accumulation of susceptible target cells during treatment. The basic reproductive ratio (R0) for the spread of SIV infection in vivo, which represents the number of productively infected cells derived from each productively infected cell at the beginning of infection, was also estimated. This parameter quantifies the extent to which antiviral therapy or vaccination must limit the initial spread of virus to prevent establishment of chronic disseminated infection. The results thus provide an important guide for efforts to develop vaccines against SIV and, by extension, human immunodeficiency virus. 相似文献
1000.
A new hybrid automatic repeat request scheme employing packet combining based on the Viterbi decoder is presented. It is shown that the proposed form of combining, together with a rearrangement of the signal constellation, can outperform similar forms of packet combining such as average diversity combining 相似文献