全文获取类型
收费全文 | 9661篇 |
免费 | 60篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 28篇 |
化学工业 | 443篇 |
金属工艺 | 115篇 |
机械仪表 | 70篇 |
建筑科学 | 100篇 |
矿业工程 | 4篇 |
能源动力 | 68篇 |
轻工业 | 281篇 |
水利工程 | 18篇 |
石油天然气 | 9篇 |
无线电 | 243篇 |
一般工业技术 | 445篇 |
冶金工业 | 7541篇 |
原子能技术 | 37篇 |
自动化技术 | 326篇 |
出版年
2021年 | 18篇 |
2019年 | 26篇 |
2018年 | 28篇 |
2017年 | 24篇 |
2016年 | 27篇 |
2015年 | 25篇 |
2014年 | 36篇 |
2013年 | 140篇 |
2012年 | 49篇 |
2011年 | 92篇 |
2010年 | 77篇 |
2009年 | 77篇 |
2008年 | 86篇 |
2007年 | 82篇 |
2006年 | 69篇 |
2005年 | 51篇 |
2004年 | 72篇 |
2003年 | 72篇 |
2002年 | 58篇 |
2001年 | 55篇 |
2000年 | 57篇 |
1999年 | 271篇 |
1998年 | 2522篇 |
1997年 | 1418篇 |
1996年 | 915篇 |
1995年 | 499篇 |
1994年 | 412篇 |
1993年 | 497篇 |
1992年 | 77篇 |
1991年 | 90篇 |
1990年 | 95篇 |
1989年 | 71篇 |
1988年 | 84篇 |
1987年 | 90篇 |
1986年 | 88篇 |
1985年 | 83篇 |
1984年 | 47篇 |
1983年 | 61篇 |
1982年 | 69篇 |
1981年 | 80篇 |
1980年 | 131篇 |
1979年 | 61篇 |
1978年 | 62篇 |
1977年 | 194篇 |
1976年 | 339篇 |
1975年 | 50篇 |
1974年 | 27篇 |
1973年 | 23篇 |
1972年 | 18篇 |
1970年 | 17篇 |
排序方式: 共有9728条查询结果,搜索用时 15 毫秒
41.
We study the nonlinear propagation of light in optical fibers in the strong nonlinearity limit. In this limit, the transverse guiding properties are altered and cannot be decoupled from the longitudinal part of the wave equation. We consider a refractive index profile with no bound modes at low intensities and show that stable self-guiding occurs at a critical intensity. This critical intensity is a property of the guide and can be made much lower than the threshold for unstable self-focusing. We consider a particular design for which self-guiding occurs at three orders of magnitude lower than the self-focusing threshold. 相似文献
42.
Cooper M. Lynne; Wood Phillip K.; Orcutt Holly K.; Albino Austin 《Canadian Metallurgical Quarterly》2003,84(2):390
Longitudinal data from a representative sample of 1,978 Black and White adolescents were used to examine the role of personality in multiple risk or problem behaviors. Results indicate that covariation among diverse behaviors (educational underachievement, delinquent behavior, substance use, sexual behavior) can be adequately modeled by a single higher order factor, and that impulsivity and avoidance coping serve as generalized risk factors for involvement in these behaviors. Whereas none of the personality variables examined explained change in problem behaviors once established, avoidance coping prospectively predicted involvement among a subgroup of adolescents with little or no prior involvement. Results suggest that dysfunctional styles of regulating emotions and emotionally driven behaviors are core features of risky or problem behaviors during adolescence. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
43.
44.
Obtaining shorter regular expressions from finite-state automata 总被引:1,自引:0,他引:1
We consider the use of state elimination to construct shorter regular expressions from finite-state automata (FAs). Although state elimination is an intuitive method for computing regular expressions from FAs, the resulting regular expressions are often very long and complicated. We examine the minimization of FAs to obtain shorter expressions first. Then, we introduce vertical chopping based on bridge states and horizontal chopping based on the structural properties of given FAs. We prove that we should not eliminate bridge states until we eliminate all non-bridge states to obtain shorter regular expressions. In addition, we suggest heuristics for state elimination that leads to shorter regular expressions based on vertical chopping and horizontal chopping. 相似文献
45.
46.
TG Orsière MM Chauvet MH Dell''Amico MJ Bourdeaux 《Canadian Metallurgical Quarterly》1995,291(3):237-243
Hepatocyte growth factor (HGF) is a potent mitogen for the maturation of hepatocytes in vitro which plays a role in liver regeneration in vivo. In addition, transforming growth factor-beta 1 (TGF-beta 1) is also a potent regulator of liver regeneration. In attempting to clarify the mechanisms related to liver regeneration after partial hepatectomy, we investigated the expression of HGF and TGF-beta 1 in rats with liver cirrhosis (LC). A rat model of LC was prepared using carbon tetrachloride (CCl4). The expression of HGF mRNA in both the LC and control groups showed a similar time-course with the highest expression seen at 18h after a 70% hepatectomy. The expression of TGF-beta 1 mRNA peaked at 18h after partial hepatectomy in the LC group and at 48h in the control group. The 5-bromo-2'-deoxyuridine (BrdU) labeling index for the LC group at 24, 48, and 72 h after partial hepatectomy was 9.2%, 5.9%, and 1.8%, while for the control group it was 7.0%, 11.7%, and 6.8%, respectively. The BrdU labeling index in the LC group was thus suppressed earlier than that in the control group. We therefore postulate that regeneration of the remnant liver in the presence of LC accelerates immediately after partial hepatectomy, but the extent of regeneration is insufficient because of an early cessation due to an early expression of TGF-beta 1. 相似文献
47.
MJ Rosen 《Canadian Metallurgical Quarterly》1995,1(3):216-222
Pneumocystis carinii pneumonia has long been considered the predominant pulmonary disease in patients with HIV, but several factors are changing this perception. The population infected with HIV is increasingly composed of injection drug users, and racial and ethnic minorities, which represent groups that have a high incidence of bacterial pneumonia and tuberculosis. The increased longevity attributed to antiretroviral therapy and P. carinii pneumonia prophylaxis is accompanied by more profound immunosuppression, rendering patients susceptible to Pseudomonas, Aspergillus, and other opportunistic pneumonias. Trimetrexate and atovaquone are now available for the treatment of P. carinii pneumonia. Both are less effective than standard regimens of trimethoprim-sulfamethoxazole, but have fewer adverse effects. The diagnosis of respiratory infections complicating HIV usually depends on isolation of the pathogen. The routine use of transbronchial biopsy during bronchoscopy is controversial because the prevalence of P. carinii pneumonia is high in most centers caring for patients with AIDS, and bronchoalveolar lavage is usually diagnostic in this disease. However, biopsy enhances the yield of bronchoscopy, especially in the diagnosis of noninfectious pulmonary disorders and infections other than P. carinii pneumonia. 相似文献
48.
Dapsone has clinical utility as an anti-inflammatory agent but the mechanism of this action remains unknown. We have previously reported that dapsone inhibits beta2 integrin (CD11b/CD18)-mediated adherence of human neutrophils in vitro and now describe studies designed to discover how dapsone-mediated inhibition of this neutrophil function occurs. Results indicate that dapsone interferes with the activation or function of the G-protein (Gi type) that initiates the signal transduction cascade common to chemotactic stimuli. They also show that dapsone-mediated suppression of this pathway inhibits the generation of second messengers essential to the activation of beta2 integrin molecules, as well as respiratory and secretory functions of neutrophils exposed to chemoattractants. We propose that the inhibition of chemoattractant-induced signal transduction by dapsone suppresses neutrophil recruitment and local production of toxic respiratory and secretory products in the affected skin of dermatitis herpetiformis and other neutrophilic dermatoses. 相似文献
49.
M Eberstadt B Huang Z Chen RP Meadows SC Ng L Zheng MJ Lenardo SW Fesik 《Canadian Metallurgical Quarterly》1998,392(6679):941-945
When activated, membrane-bound receptors for Fas and tumour-necrosis factor initiate programmed cell death by recruiting the death domain of the adaptor protein FADD to the membrane. FADD then activates caspase 8 (also known as FLICE or MACH) through an interaction between the death-effector domains of FADD and caspase 8. This ultimately leads to the apoptotic response. Death-effector domains and homologous protein modules known as caspase-recruitment domains have been found in several proteins and are important regulators of caspase (FLICE) activity and of apoptosis. Here we describe the solution structure of a soluble, biologically active mutant of the FADD death-effector domain. The structure consists of six antiparallel, amphipathic alpha-helices and resembles the overall fold of the death domains of Fas and p75. Despite this structural similarity, mutations that inhibit protein-protein interactions involving the Fas death domain have no effect when introduced into the FADD death-effector domain. Instead, a hydrophobic region of the FADD death-effector domain that is not present in the death domains is vital for binding to FLICE and for apoptotic activity. 相似文献
50.
MJ Snowling 《Canadian Metallurgical Quarterly》1996,313(7065):1096-1097