全文获取类型
收费全文 | 6923篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 43篇 |
金属工艺 | 5篇 |
机械仪表 | 2篇 |
建筑科学 | 7篇 |
能源动力 | 4篇 |
轻工业 | 85篇 |
水利工程 | 6篇 |
石油天然气 | 2篇 |
无线电 | 6篇 |
一般工业技术 | 31篇 |
冶金工业 | 6713篇 |
原子能技术 | 1篇 |
自动化技术 | 19篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 12篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 16篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 8篇 |
2009年 | 12篇 |
2008年 | 8篇 |
2007年 | 9篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 7篇 |
2003年 | 13篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 213篇 |
1998年 | 2305篇 |
1997年 | 1283篇 |
1996年 | 810篇 |
1995年 | 422篇 |
1994年 | 340篇 |
1993年 | 415篇 |
1992年 | 37篇 |
1991年 | 47篇 |
1990年 | 53篇 |
1989年 | 47篇 |
1988年 | 54篇 |
1987年 | 56篇 |
1986年 | 53篇 |
1985年 | 36篇 |
1984年 | 1篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 31篇 |
1980年 | 61篇 |
1979年 | 3篇 |
1978年 | 13篇 |
1977年 | 136篇 |
1976年 | 277篇 |
1975年 | 11篇 |
1973年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有6935条查询结果,搜索用时 15 毫秒
61.
62.
The sex ratio produced by an individual may be a consequence of relative frequencies of genotypes amongst offspring, or may result directly from parental (maternal) control. We analyse the evolutionarily stable sex ratio for a hypothetical organism in which both forms of sex ratio expression can occur. We prove that the point of expression of sex ratio does not affect the evolutionarily stable sex ratio for diploid hosts in populations infected with cytoplasmically inherited sex ratio distorters. 相似文献
63.
64.
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
65.
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
66.
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
67.
SJ Mihic Q Ye MJ Wick VV Koltchine MD Krasowski SE Finn MP Mascia CF Valenzuela KK Hanson EP Greenblatt RA Harris NL Harrison 《Canadian Metallurgical Quarterly》1997,389(6649):385-389
Volatile anaesthetics have historically been considered to act in a nonspecific manner on the central nervous system. More recent studies, however, have revealed that the receptors for inhibitory neurotransmitters such as gamma-aminobutyric acid (GABA) and glycine are sensitive to clinically relevant concentrations of inhaled anaesthetics. The function of GABA(A) and glycine receptors is enhanced by a number of anaesthetics and alcohols, whereas activity of the related GABA rho1 receptor is reduced. We have used this difference in pharmacology to investigate the molecular basis for modulation of these receptors by anaesthetics and alcohols. By using chimaeric receptor constructs, we have identified a region of 45 amino-acid residues that is both necessary and sufficient for the enhancement of receptor function. Within this region, two specific amino-acid residues in transmembrane domains 2 and 3 are critical for allosteric modulation of both GABA(A) and glycine receptors by alcohols and two volatile anaesthetics. These observations support the idea that anaesthetics exert a specific effect on these ion-channel proteins, and allow for the future testing of specific hypotheses of the action of anaesthetics. 相似文献
68.
Coupling GIS with Hydrologic and Hydraulic Flood Modelling 总被引:6,自引:1,他引:5
Nunes Correia Francisco Castro Rego Filipe Da Grača Saraiva Maria Ramos Isabel 《Water Resources Management》1998,12(3):229-249
Geographic Information Systems (GIS) have been recognised as a powerful means to integrate and analyse data from various sources in the context of comprehensive floodplain management. As part of this comprehensive approach to floodplain management, it is very important to be able to predict the consequences of different scenarios in terms of flooded areas and associated risk. Hydrologic and hydraulic modelling plays a crucial role and there is much to gain in incorporating these modelling capabilities in GIS. This is still a rather complex task and research is being done on the full integration of these models. Interfacing between these models and GIS may be a very efficient way of overcoming the difficulties and getting very good results in terms of engineering practice. This paper presents results based on the use of Intergraph GIS coupled with Idrisi GIS. Using these two systems substantially increased the flexibility of using GIS as a tool for flood studies. A lumped (XSRAIN) and a distributed (OMEGA) hydrologic models were used to simulate flood hydrographs. The well known HEC-2 Hydraulic model was used to compute flooded areas. These models were applied in the Livramento catchment with very good results. The computation of flooded areas for different flood scenarios, and its representation in GIS, can be used in the assessment of affected property and associated damages. This is a very useful GIS-based approach to floodplain management. 相似文献
69.
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
70.
MJ Snowling 《Canadian Metallurgical Quarterly》1996,313(7065):1096-1097