全文获取类型
收费全文 | 8283篇 |
免费 | 532篇 |
国内免费 | 20篇 |
专业分类
电工技术 | 111篇 |
综合类 | 10篇 |
化学工业 | 1670篇 |
金属工艺 | 195篇 |
机械仪表 | 262篇 |
建筑科学 | 243篇 |
矿业工程 | 7篇 |
能源动力 | 293篇 |
轻工业 | 630篇 |
水利工程 | 73篇 |
石油天然气 | 43篇 |
无线电 | 1081篇 |
一般工业技术 | 1925篇 |
冶金工业 | 944篇 |
原子能技术 | 41篇 |
自动化技术 | 1307篇 |
出版年
2024年 | 22篇 |
2023年 | 83篇 |
2022年 | 155篇 |
2021年 | 259篇 |
2020年 | 201篇 |
2019年 | 189篇 |
2018年 | 241篇 |
2017年 | 251篇 |
2016年 | 285篇 |
2015年 | 234篇 |
2014年 | 331篇 |
2013年 | 563篇 |
2012年 | 524篇 |
2011年 | 636篇 |
2010年 | 483篇 |
2009年 | 473篇 |
2008年 | 493篇 |
2007年 | 397篇 |
2006年 | 346篇 |
2005年 | 280篇 |
2004年 | 243篇 |
2003年 | 222篇 |
2002年 | 185篇 |
2001年 | 159篇 |
2000年 | 133篇 |
1999年 | 118篇 |
1998年 | 194篇 |
1997年 | 156篇 |
1996年 | 124篇 |
1995年 | 101篇 |
1994年 | 100篇 |
1993年 | 85篇 |
1992年 | 70篇 |
1991年 | 60篇 |
1990年 | 49篇 |
1989年 | 41篇 |
1988年 | 36篇 |
1987年 | 38篇 |
1986年 | 28篇 |
1985年 | 35篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 24篇 |
1981年 | 28篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1977年 | 13篇 |
1976年 | 20篇 |
1975年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有8835条查询结果,搜索用时 15 毫秒
51.
Handley Simon J.; Evans Jonathan St. B. T.; Thompson Valerie A. 《Canadian Metallurgical Quarterly》2006,32(3):559
Under the suppositional account of conditionals, when people think about a conditional assertion, "if p then q," they engage in a mental simulation in which they imagine p holds and evaluate the probability that q holds under this supposition. One implication of this account is that belief in a conditional equates to conditional probability [P(q/p)]. In this paper, the authors examine a further implication of this analysis with respect to the wide-scope negation of conditional assertions, "it is not the case that if p then q." Under the suppositional account, nothing categorically follows from the negation of a conditional, other than a second conditional, "if p then not-q." In contrast, according to the mental model theory, a negated conditional is consistent only with the determinate state of affairs, p and not-q. In 4 experiments, the authors compare the contrasting predictions that arise from each of these accounts. The findings are consistent with the suppositional theory but are incongruent with the mental model theory of conditionals. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
52.
Takuma Suzuki Hang-Ju Ko Agus Setiawan Jung-Jin Kim Koh Saitoh Masami Terauchi Takafumi Yao 《Materials Science in Semiconductor Processing》2003,6(5-6):519-521
We report the successful growth of Ga-polar GaN epilayers on O-polar ZnO templates pre-deposited on c-sapphire. Prior to GaN growth, NH3 is exposed onto the ZnO template. The polarity of the GaN layers is confirmed by etching of the surface and by conversion beam electron diffraction (CBED), while the O-polar ZnO is confirmed by CBED. It is suggested that the NH3 pre-exposure helps form a Zn3N2 layer, which possesses inversion symmetry and inverts the crystal from anion polar to cation polar. 相似文献
53.
Dynamic RSVP protocol 总被引:5,自引:0,他引:5
Geng-Sheng Kuo Po-Chang Ko 《Communications Magazine, IEEE》2003,41(5):130-135
RSVP is a resource reservation setup protocol that can be used by a host to request specific QoS for multicast multimedia flows on the Internet. Multiprotocol label switching (MPLS) architecture also needs RSVP. The fact that the resolutions of the display system used in different receiver nodes might have different, multi-resolution characteristics is supported in the MPEG-4 standard, and the EZW compression algorithm can cease decoding at any point in the bitstream. However, RSVP does not provide a more flexible mechanism. In this article we propose an extension of RSVP to provide the needed mechanism, coined dynamic RSVP (DRSVP), to dynamically adjust reserved resources on nodes without much effort. It provides different video resolutions to different receiver nodes with different needed reserved resources. Therefore, it does not waste precious Internet resources to transmit unnecessary multimedia packets. 相似文献
54.
Voucher-based reinforcement therapy (VBRT) is an effective drug abuse treatment, but the cost of VBRT rewards has limited its dissemination. Obtaining VBRT incentives through donations may be one way to overcome this barrier. Two direct mail campaigns solicited donations for use in VBRT for pregnant, postpartum, and parenting drug users in Toronto, Ontario, Canada, and in Los Angeles, California. In Toronto, 19% of those contacted over 2 months donated $8,000 ($4,000/month) of goods and services. In Los Angeles, nearly 26% of those contacted over 34 months donated $161,000 ($4,472/month) of goods and services. Maintaining voucher programs by soliciting donations is feasible and sustainable. The methods in this article can serve as a guide for successful donation solicitation campaigns. Donations offer an alternative for obtaining VBRT rewards for substance abuse treatment and may increase its dissemination. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
55.
A reinjection experiment has been conducted in an attempt to sustain reservoir pressure and steam production and to extract remaining heat energy in the superheated reservoir in the Matsukawa vapor-dominated geothermal field. This experiment was undertaken because the increase in superheat of produced steam and the decline of steam production are the current major issues for stable operation of the power plant. Almost all the reinjected fluid into well MR 1 was recovered from well M5, and the steam production of well M5 has increased by approximately 67%. 相似文献
56.
An important aspect of the vehicle routing problem (VRP) that has been largely overlooked is the use of satellite facilities to replenish vehicles during a route. When possible, satellite replenishment allows the drivers to continue making deliveries until the close of their shift without necessarily returning to the central depot. This situation arises primarily in the distribution of fuels and certain retail items. When demand is random, optimizing customer routes a priori may result in significant additional costs for a particular realization of demand. Satellite facilities are one way of safeguarding against unexpected demand. This paper presents a branch and cut methodology for solving the VRP with satellite facilities subject to capacity and route time constraints. We begin with a mixed-integer linear programming formulation and then describe a series of valid inequalities that can be used to cut off solutions to the linear programming relaxation. Several separation heuristics are then outlined that are used to generate the cuts. Embedded in the methodology is a VRP heuristic for finding good feasible solutions at each stage of the computations. Results are presented for a set of problems derived from our experience with a leading propane distributor. 相似文献
57.
Peter J. Bentley Jonathan P. Wakefield 《Computer-Aided Civil and Infrastructure Engineering》1996,11(3):153-161
Abstract: This paper examines the first stage of using genetic algorithms in design—how to encode designs as chromosomes. Generic representations capable of describing the geometry of any solid object to eliminate the unnecessary duplication of work at this stage are explored. A suitable low-parameter, spatial-partitioning representation is then proposed, using partitions consisting of six-sided polyhedra intersected by planes. Finally, the coding of the representation is examined, with the conclusion that allelic coding with control genes and user-definable, fixed-value alleles would provide the most flexible system. 相似文献
58.
Assaderaghi F. Chen J. Solomon R. Chian T.-Y. Ko P.K. Hu C. 《Electron Device Letters, IEEE》1991,12(10):518-520
It has been found that the subthreshold currents of fully depleted silicon-on-insulator (SOI) MOSFETs show a transient behavior under certain front-gate and back-gate voltage conditions. The cause of this anomaly is explained, and applications for the phenomenon are pointed out. Particularly, a simple way to measure the silicon film thickness is suggested 相似文献
59.
The purpose of this study was to evaluate the relationship between the number of yolk sacs and amnionicity in monochorionic twin pregnancies scanned early in the first trimester. We retrospectively reviewed images of all monochorionic twins scanned between 6 and 9.5 weeks' gestation and with pathologic or sonographic confirmation of chorionicity-amnionicity. Each film was reviewed for the number of yolk sacs present, as well as for the gestational age at which the amniotic membrane was first visualized. Twenty monochorionic-diamniotic pregnancies and two monochorionic-monoamniotic pregnancies met the criteria for inclusion in the study. In diamniotic pregnancies scanned at less than 8 weeks' gestation, only the yolk sacs were identified; none of the dividing amniotic membranes were detected. Two yolk sacs were identified in all but one case. In this case, although one yolk sac was seen at 6 weeks, follow-up scanning at 8 weeks revealed two yolk sacs. In each of the monochorionic-monoamniotic twin pregnancies, one yolk sac was seen at 9 weeks and a single amnion encircled both embryos. We conclude that the sonographic identification of two yolk scas in monochorionic twins enables us to make the diagnosis of diamniotic twins early in the first trimester, before the amniotic membrane can be imaged. The presence of one yolk sac should prompt a follow-up ultrasonogram to assign amnionicity definitively. 相似文献
60.