全文获取类型
收费全文 | 9562篇 |
免费 | 107篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 83篇 |
综合类 | 16篇 |
化学工业 | 690篇 |
金属工艺 | 92篇 |
机械仪表 | 110篇 |
建筑科学 | 189篇 |
矿业工程 | 30篇 |
能源动力 | 87篇 |
轻工业 | 524篇 |
水利工程 | 57篇 |
石油天然气 | 22篇 |
武器工业 | 1篇 |
无线电 | 628篇 |
一般工业技术 | 768篇 |
冶金工业 | 5642篇 |
原子能技术 | 49篇 |
自动化技术 | 693篇 |
出版年
2021年 | 58篇 |
2020年 | 38篇 |
2019年 | 76篇 |
2018年 | 72篇 |
2017年 | 52篇 |
2016年 | 58篇 |
2015年 | 50篇 |
2014年 | 81篇 |
2013年 | 233篇 |
2012年 | 133篇 |
2011年 | 189篇 |
2010年 | 143篇 |
2009年 | 138篇 |
2008年 | 194篇 |
2007年 | 191篇 |
2006年 | 172篇 |
2005年 | 166篇 |
2004年 | 131篇 |
2003年 | 114篇 |
2002年 | 124篇 |
2001年 | 122篇 |
2000年 | 99篇 |
1999年 | 240篇 |
1998年 | 1697篇 |
1997年 | 1019篇 |
1996年 | 618篇 |
1995年 | 432篇 |
1994年 | 364篇 |
1993年 | 377篇 |
1992年 | 134篇 |
1991年 | 94篇 |
1990年 | 137篇 |
1989年 | 133篇 |
1988年 | 121篇 |
1987年 | 111篇 |
1986年 | 101篇 |
1985年 | 119篇 |
1984年 | 75篇 |
1983年 | 65篇 |
1982年 | 66篇 |
1981年 | 67篇 |
1980年 | 78篇 |
1979年 | 63篇 |
1978年 | 66篇 |
1977年 | 157篇 |
1976年 | 306篇 |
1975年 | 62篇 |
1974年 | 37篇 |
1973年 | 37篇 |
1972年 | 36篇 |
排序方式: 共有9681条查询结果,搜索用时 12 毫秒
11.
A rare case associated with congenital hematometrocolpos in a circumcised 13 years old Somalian girl is presented. Emphasis on proper history is highlighted. Mutilation caused by bad cultural practice of female circumcision which is although not a problem in Pakistan, is brought into notice for those who may be unaware of perineal appearance of a circumcised female and stitched over vagina. 相似文献
12.
M Simion SA Jovanovic P Trisi A Scarano A Piattelli 《Canadian Metallurgical Quarterly》1998,18(1):8-23
This study investigated the effect on vertical bone regeneration of the addition of demineralized freeze-dried bone allograft or autogenous bone chips to a membrane technique. Twenty partially edentulous patients with vertical jawbone deficiencies were selected for this study. The patients were divided into two groups of 10 individuals. The 10 patients of Group A received 26 Br?nemark implants in 10 surgical sites. The 10 patients of Group B received 32 implants in 12 surgical sites. Fifty-two out of 58 implants (22 in Group A and 30 in Group B) extended 1.5 to 7.5 mm superior to the bone crest. Titanium-reinforced expanded polytetrafluoroethylene membranes were used to cover the implants and, before complete membrane fixation, demineralized freeze-dried bone allograft particles were condensed under the membrane in Group A, and autogenous bone chips were used in Group B. At the reentry after 7 to 11 months the membranes were removed and a small biopsy was collected from 11 sites comprehending the miniscrews. The clinical measurements from Group A demonstrated a mean vertical bone gain of 3.1 mm (SD = 0.9 mm, range 1 to 5 mm) with a mean percentage of bone gain of 124% (SD = 46.6%). The measurements from Group B showed a mean vertical bone gain of 5.02 mm (SD = 2.3 mm, range 1 to 8.5 mm) with a mean percentage of bone gain of 95% (SD = 26.8%). Histomorphometric analysis of the present study clearly demonstrated a direct correlation between the density of the pre-existing bone and the density of the regenerated bone. The mean percentage of new bone-titanium contact was from 39.1% to 63.2%, depending on the quality of the pre-existing bone. Both the clinical and histologic results indicate a beneficial effect of the addition of demineralized freeze-dried bone allograft or autogenous bone particles to vertical ridge augmentation procedures in humans. 相似文献
13.
The purpose of this study was to identify family physicians' firearm safety counseling beliefs and behaviors. A survey was mailed to a random sample of 600 members of the American Academy of Family Physicians. A three wave mailing technique was used to maximize the response rate and yielded 271 usable surveys (55% response rate). Outcome measures included training experience in firearm safety counseling, the prevalence of firearm safety counseling by family physicians, and their perceptions regarding such counseling. The majority (78%) of family physicians lacked formal training on how to counsel patients about firearm safety and 49% believed more time should be spent in residency programs on firearm safety counseling. The majority (84%) of respondents never or rarely counseled patients on firearm safety and 50% believed firearm safety counseling should be a low priority in their delivery of primary care. The majority of respondents did not regularly counsel patients about firearm safety, did not believe firearm safety counseling should be a priority, and did not believe firearm safety counseling would be effective in reducing firearm-related trauma. 相似文献
14.
The MSMIE protocol [SBC89] allows processors in a distributed system to communicate via shared memory. It was designed to meet the reliability and efficiency needs of applications such as nuclear safety systems. We present a formal model of the MSMIE protocol expressed in the notation CCS. Desirable properties of the protocol are expressed in the modal mu-calculus, an expressive modal logic. We show that the protocol lacks an important liveness property. In actual operation, additional operating constraints are checked to avoid potential problems. We present a modified protocol and show that it possesses the liveness property even without checking operating constraints. We also show how parts of the analysis were automated with the Concurrency Workbench. 相似文献
15.
In 3 experiments, participants memorized 8 examples, each exemplifying a different rule. Participants were asked to extend these rules to new examples. They practiced applications of the rules to examples over a period of 4 days (Experiment 1) or 5 days (Experiments 2 and 3). Although these rules were bidirectional, an asymmetry gradually built up such that participants became more facile in using the rules in the practiced direction. Participants also showed an advantage when the initial study example was repeated or when test examples were repeated. It is argued that skill acquisition involves development of a complex set of strategies based on use of rules and retrieval of examples. Four overlapping stages of skill acquisition are described. 相似文献
16.
D.L Orphal C.E Anderson Jr. R.R Franzen J.D Walker P.N Schneidewind M.E Majerus 《International Journal of Impact Engineering》1993,14(1-4):551-560
Calculations of steel target penetration by L/D ≤ 1 tungsten and tungsten alloy projectiles have been extended to L/D = 1/32 over the velocity range 1.5 to 5 km/s. The ratio of crater to projectile diameter tends to 1 as L/D decreases over this entire velocity range. For impact velocities of 1.5 and 3 km/s, penetration depth normalized by projectile length, P/L, increases with decreasing projectile L/D up to a maximum value and then decreases for still lower L/D. Experiments at impact velocities of 2 and 3 km/s confirm these results. For 5 km/s impact velocity, the calculations show P/L increasing with decreasing projectile L/D over the entire range 1/32 ≤ L/D ≤ 1. The projectile L/D for which the maximum P/L occurs appears to depend on the impact velocity. P/L generally scales with impact velocity as P/L vf(L/D) where f(L/D) ranges from 0 for a long rod to, we believe, 2 in the limit as projectile L/D approaches zero. The calculations show for 1/8 ≤ L/D ≤ 1/2, P/L v0.9; for L/D = 1/16, P/L v1.5; and for L/D = 1/32, the new results give P/L v1.9. 相似文献
17.
Q Hu M Trevisan Y Xu W Dong SA Berger SD Lyman MD Minden 《Canadian Metallurgical Quarterly》1995,95(6):2530-2538
The growth of human leukemic cells in culture and in vivo is dependent upon the presence of hematopoietic growth factors. Most populations of human leukemic acute myeloblastic leukemia (AML) cells express c-Kit on their surface and respond to Kit ligand (KL) in culture. To determine if this interaction was of potential significance in vivo we used a mouse model system. 32D cells, a murine IL-3-dependent myeloid cell line, were rendered KL responsive by transfection of the murine c-Kit. After injection of 32D or 32D-Kit cells into syngeneic hosts, animals bearing 32D-Kit cells, but not 32D cells, became moribund and were killed. These animals had circulating leukemic blast cells, infiltration of bone marrow, spleen, brain, liver, lung, and kidney. Cells recovered from some of the animals continued to be dependent upon IL-3 or KL for growth while in other cases the cells were factor independent. This model illustrates that the constitutive expression of c-Kit enhances the leukemic potential of 32D cells. The model will be useful for studying the progression of leukemia in vivo and testing whether interruption of the interaction of Kit and KL can affect the growth of leukemic cells. 相似文献
18.
19.
A novel enzymatic reaction involved in the metabolism of aliphatic epoxides by Xanthobacter strain Py2 is described. Cell extracts catalyzed the CO2-dependent carboxylation of propylene oxide (epoxypropane) to form acetoacetate and beta-hydroxybutyrate. The time courses of acetoacetate and beta-hydroxybutyrate formaton indicate that acetoacetate is the primary product of propylene oxide carboxylation and that beta-hydroxybutyrate is a secondary product formed by the reduction of acetoacetate. Analogous C5 carboxylation products were identified with 1,2-epoxybutane as the substrate. In the absence of CO2, propylene oxide and 1,2-epoxybutane were isomerized to form acetone and methyl ethyl ketone, respectively, as dead-end products. The carboxylation of short-chain epoxides to beta-keto acids is proposed to serve as the physiological reaction for the metabolism of aliphatic epoxides in Xanthobacter strain Py2. 相似文献
20.
SA Anish 《Canadian Metallurgical Quarterly》1993,90(8):599-601
A 56-year-old male presented with clinical and serological data suggestive of Lyme disease. The patient was found to have an aortic valvular vegetation by transesophageal echocardiography. This report represents the first case of Lyme disease with possible valvular involvement. 相似文献