全文获取类型
收费全文 | 5658篇 |
免费 | 83篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 49篇 |
综合类 | 2篇 |
化学工业 | 578篇 |
金属工艺 | 107篇 |
机械仪表 | 56篇 |
建筑科学 | 121篇 |
矿业工程 | 27篇 |
能源动力 | 59篇 |
轻工业 | 315篇 |
水利工程 | 24篇 |
石油天然气 | 3篇 |
无线电 | 323篇 |
一般工业技术 | 614篇 |
冶金工业 | 3093篇 |
原子能技术 | 40篇 |
自动化技术 | 335篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 57篇 |
2020年 | 34篇 |
2019年 | 53篇 |
2018年 | 59篇 |
2017年 | 55篇 |
2016年 | 54篇 |
2015年 | 39篇 |
2014年 | 68篇 |
2013年 | 159篇 |
2012年 | 111篇 |
2011年 | 147篇 |
2010年 | 114篇 |
2009年 | 104篇 |
2008年 | 110篇 |
2007年 | 96篇 |
2006年 | 109篇 |
2005年 | 81篇 |
2004年 | 73篇 |
2003年 | 83篇 |
2002年 | 80篇 |
2001年 | 75篇 |
2000年 | 66篇 |
1999年 | 150篇 |
1998年 | 973篇 |
1997年 | 609篇 |
1996年 | 388篇 |
1995年 | 211篇 |
1994年 | 186篇 |
1993年 | 203篇 |
1992年 | 62篇 |
1991年 | 51篇 |
1990年 | 51篇 |
1989年 | 75篇 |
1988年 | 70篇 |
1987年 | 45篇 |
1986年 | 46篇 |
1985年 | 37篇 |
1984年 | 25篇 |
1983年 | 24篇 |
1982年 | 24篇 |
1981年 | 29篇 |
1980年 | 32篇 |
1979年 | 21篇 |
1978年 | 32篇 |
1977年 | 92篇 |
1976年 | 209篇 |
1975年 | 32篇 |
1974年 | 21篇 |
排序方式: 共有5746条查询结果,搜索用时 15 毫秒
961.
AG van der Zee EM de Cuyper PC Limburg HW de Bruijn H Hollema J Bijzet M Krans EG de Vries 《Canadian Metallurgical Quarterly》1995,75(4):1004-1009
BACKGROUND: Recently, high pretreatment platelet counts and low pretreatment hemoglobin levels were found to be negative prognostic factors in patients with ovarian cancer. Interleukin-6 (IL-6) is a multifunctional cytokine with a diversity of functions leading to the induction of C-reactive protein (CRP), increased platelet counts, and low hemoglobin levels. Different epithelial ovarian cancer cell lines are found to produce varying amounts of IL-6. In this study, a possible relationship between IL-6 levels in cystic fluids of benign and malignant ovarian tumors and pretreatment serum CRP, platelet counts, and hemoglobin levels was evaluated. METHODS: A bioassay and enzyme-linked immunosorbent assay (ELISA) were performed to determine the IL-6 levels in cystic fluids and serum from 42 patients with benign and malignant ovarian tumors. RESULTS: The median IL-6 level was higher in cystic fluids of malignant tumors (n = 21) when compared with cystic fluids of benign tumors (n = 21) (P < 0.01 for bioassay and ELISA). Serum IL-6 levels in patients with malignant tumors were not significantly higher compared with IL-6 levels in patients with benign tumors, whereas CRP levels were higher in patients with malignant tumors (P < 0.01). Cystic fluid IL-6 levels were related to serum CRP levels (r = 0.60, P < 0.01 [bioassay]; r = 0.41, P < 0.01 [ELISA]), and were related inversely to hemoglobin levels (r = -0.57, P < 0.01 [bioassay]; r = 0.54, P < 0.01 [ELISA]). CONCLUSIONS: IL-6 levels are higher in cystic fluids of malignant ovarian tumors compared with benign tumors. The relationship of cystic fluid IL-6 levels with CRP, platelet counts, and hemoglobin levels suggests a possible causative role of tumor-derived IL-6 in the appearance of general side effects of ovarian cancer, which recently have been recognized as prognostic factors. 相似文献
962.
Jürgen Vollmar Rainer Eckrich Stefan Lotz Kurt Marchetti Hans-Joachim Mayer Manfred Rammo Ronald Ritter Guntram Wagner Wolfgang Guth 《工业材料与腐蚀》1992,43(10):475-482
Corrosion fatigue behaviour of steel Ck 45 in aqueous solutions containing chloride ions The fatigue behaviour of carbon steel Ck 45 (comparable to AISI 1045x) is investigated for cyclic tension and rotating bending load with a frequency of 25 Hz. The fatigue limits under cyclic tension load in air are 410 N/mm2 for smooth specimens and 290 N/mm2 for notched specimens. For rotating bending load a value of 200 N/mm2 is found for smooth specimen. The fatigue limits for N = 107 in two different environments (0.3% and 3% NaCl-solution) reach only 37–57% of the according values in air. Cathodic protection of smooth specimens causes an improvement to 95% of the air fatigue limit. The evaluation of the free corrosion potential for all corrosion fatigue tests and the appearence of fracture show typical attributes of corrosion fatigue in the active state. 相似文献
963.
EM Krupitski? AM Burakov AIa Grinenko IuS Borodkin 《Canadian Metallurgical Quarterly》1995,95(6):67-71
90 alcoholic patients (II stage of alcoholism) with secondary affective disorders (anxiety, depression) were divided into 4 groups. The patients of the first group received the GABA receptor ligand baclofen during 3 weeks. Sybazon preparation was used in the second group, while the patients of the third group were treated with amitriptyline. Placebo was applied in the forth group. The clinical psychological tests demonstrated that all drugs caused quite effective relief of affective disorders. Psychosemantic tests application showed that the pharmacotherapy caused positive changes in patients of 1-3 groups. These changes touched on both system of personal estimations and relations of personality to himself and to the world around i.e. psychosemantic sphere. Such changes in psychosemantic sphere were not observed in the 4-th group of patients (placebo). Besides it was revealed that each drug caused some specific changes in psychosemantic sphere. The result obtained were supposed to have some theoretical value in comprehension of brain-psychics relations as well as the applied significance for adequate choice of affective disorders pharmacotherapy of alcoholic patients. 相似文献
964.
J. D. Jorgensen P. G. Radaelli H. Shaked J. L. Wagner B. A. Hunter J. F. Mitchell R. L. Hitterman D. G. Hinks 《Journal of Superconductivity》1994,7(1):145-149
Oxygen vacancy and interstitial defects can have a profound effect on the superconducting properties of copper oxide compounds. Recent work on compounds such as La2CuO4+x
and HgBa2CuO4+x
has provided new insight into the role of interstitial oxygen defects as a doping mechanism. The number of carriers created by each interstitial defect depends on the local defect structure. Studies of (La, Sr, Ca)3Cu2O6+x
with various metal compositions and metalsite ordering show that interstitial oxygen defects that form between the CuO2 layers in this structure systematically lowerT
c
and eventually destroy superconductivity. Conversely, oxygen vacancies in the CuO2 planes have surprisingly little effect at concentrations below 3%. The infinite-layer compounds, ACuO2, where A=La, Sr, Ca, Nd, etc., in solid-solution combinations, could offer a similar environment for the formation of interstitial oxygen defects between the CuO2 planes, allowing interstitial oxygen defects to contribute to the doping of these compounds. However, neutron diffraction experiments on Sr0.9La0.1CuO2 (T
c
= 42 K) have not found any interstitial oxygen. 相似文献
965.
John B. Deaton Jr. James W. Wagner Robert S. Rogowski 《Journal of Nondestructive Evaluation》1994,13(1):13-22
An electronic speckle pattern interferometer that incorporates a commercial, long-working-distance microscope is described which provides new opportunities to perform nondestructive inspection for applications in fields such as microelectronics. The long-working-distance microscrope was attached directly to the CCD camera to form a compact, portable system with a field of view that was variable over several mm in width. Alignment was greatly simplified because the skewed Michelson interferometer configuration used a speckled reference beam imaged from a diffusely reflecting reference surface that was positioned adjacent to the test object. To demonstrate the performance of the micro-ESPI instrument, fringe patterns were recorded for the quasi-static cantilever deflection of a 1 mm-wide interconnect clip from an electronics socket. 相似文献
966.
EM Emery GP Ritter-Randolph AL Strozier RJ McDermott 《Canadian Metallurgical Quarterly》1993,41(5):195-198
Despite extensive efforts to decrease alcohol abuse among college students, prevention approaches have had limited success. This study attempted to clarify reasons for this limited success and to identify directions for future interventions by directly interviewing college students on this topic. Five issues were discussed in the focus group interviews: (1) reasons for drinking alcohol, (2) reasons for not drinking alcohol, (3) circumstances surrounding overconsumption of alcohol, (4) topics and methods for prevention, and (5) gender differences in drinking patterns. The focus group interviews were found to be a valid tool for elucidating sensitive aspects of these issues and the relative importance of these issues to each other. The students revealed how susceptible they are to societal pressures to drink alcohol and how the limitations of their intrapersonal skills affect their alcohol consumption, most notably regarding sexuality issues. The authors contend that improving intrapersonal skills should be a major focus of programs to prevent alcohol abuse. 相似文献
967.
JA Wagner H Ross S Hunt P Gamberg H Valantine TC Merigan EB Stinson 《Canadian Metallurgical Quarterly》1995,60(12):1473-1477
Cytomegalovirus (CMV) infection is associated with an increased incidence of other opportunistic infections in organ transplant recipients. Whether this is related to immunomodulating effects of CMV or independent of CMV but associated with a host risk factor common to both infections is unclear. The purpose of this study was to determine whether the reduction in CMV infections seen with prophylactic ganciclovir treatment after heart transplantation is associated with a reduced incidence of other opportunistic infections. Of 149 patients prospectively enrolled in a multicenter, randomized, double-blind, placebo-controlled trial of ganciclovir to prevent CMV disease, 74 patients enrolled at this center (33 control and 41 ganciclovir-treated) were retrospectively identified. All received prophylactic OKT-3 and standard 3 drug maintenance immunosuppressive therapy. Actuarial survival and rejection rates and incidence of opportunistic infections (bacterial, fungal, and protozoal) for the 2 treatment groups were determined and compared using Cox-Mantel analysis. CMV disease occurred 2.5 times more frequently in the control group. There were no significant differences in survival or rejection rates nor in bacterial or protozoal infection incidence between the 2 groups. Bacterial infections occurred in 54% of control and 39% of ganciclovir-treated patients (P = 0.18). There were significantly fewer fungal infections in the ganciclovir-treated group (7% vs. 27%, P = 0.0071). CMV and fungal infections were both significantly reduced in patients who received ganciclovir prophylaxis. This suggests that active CMV disease may be causally associated with the development of opportunistic fungal infections. 相似文献
968.
Quality of life is important to persons experiencing migraine. This study discusses the development of a migraine-specific quality-of-life measure (MSQOL). Participants, who included migraineurs from both tertiary care centers and the community, were screened using the International Headache Society migraine criteria prior to enrollment. Internal consistency of the MSQOL was high (alpha 0.92). Reproducibility over an average of 24 days was high (intraclass correlation 0.90). Construct validity was determined by convergent validity and known groups validity. The MSQOL was compared to two other frequently used health status questionnaires; results indicate that the MSQOL more closely resembles well-being than functional status. Results also indicate that migraineurs with more symptoms, medical appointments per year to treat migraines, and migraine episodes per year have a significantly worse quality of life. The MSQOL proved valid and reliable as a self-administered measure and will be a useful tool in clinical migraine research. The information gained from its use in the clinical environment should provide important additional information about the impact of migraine on quality of life and the potential benefits of therapeutic interventions. 相似文献
969.
T Tüting CC Wilson DM Martin YL Kasamon J Rowles DI Ma CL Slingluff SN Wagner P van der Bruggen J Baar MT Lotze WJ Storkus 《Canadian Metallurgical Quarterly》1998,160(3):1139-1147
DNA-based immunization strategies designed to elicit cellular antitumor immunity offer an attractive alternative to protein- or peptide-based approaches. In the present study we have evaluated the feasibility of DNA vaccination for the induction of CTL reactivity to five different melanoma Ags in vitro. Cultured, monocyte-derived dendritic cells (DC) were transiently transfected with plasmid DNA encoding human MART-1/Melan-A, pMel-17/gp100, tyrosinase, MAGE-1, or MAGE-3 by particle bombardment and used to stimulate autologous PBMC responder T cells. CTL reactivity to these previously identified melanoma Ags was reproducibly generated after two or three stimulations with genetically modified DC. Co-ordinate transfection of two melanoma Ag cDNAs into DC promoted CTL responders capable of recognizing epitopes from both gene products. Coinsertion of genes encoding the Th1-biasing cytokines IL-12 or IFN-alpha consistently enhanced the magnitude of the resulting Ag-specific CTL reactivity. Importantly, DC transfected with a single melanoma Ag cDNA were capable of stimulating Ag-specific CTL reactivity restricted by multiple host MHC alleles, some of which had not been previously identified. These results support the inherent strengths of gene-based vaccine approaches that do not require prior knowledge of responder MHC haplotypes or of relevant MHC-restricted peptide epitopes. Given previous observations of in situ tumor HLA allele-loss variants, DC gene vaccine strategies may elicit a greater diversity of host therapeutic immunity, thereby enhancing the clinical utility and success of such approaches. 相似文献
970.
A heterologous feline immunodeficiency virus (FIV) expression system permitted high-level expression of FIV proteins and efficient production of infectious FIV in human cells. These results identify the FIV U3 element as the sole restriction to the productive phase of replication in nonfeline cells. Heterologous FIV expression in a variety of human cell lines resulted in profuse syncytial lysis that was FIV env specific, CD4 independent, and restricted to cells that express CXCR4, the coreceptor for T-cell-line-adapted strains of human immunodeficiency virus. Stable expression of human CXCR4 in CXCR4-negative human and rodent cell lines resulted in extensive FIV Env-mediated, CXCR4-dependent cell fusion and infection. In feline cells, stable overexpression of human CXCR4 resulted in increased FIV infectivity and marked syncytium formation during FIV replication or after infection with FIV Env-expressing vectors. The use of CXCR4 is a fundamental feature of lentivirus biology independent of CD4 and a shared cellular link to infection and cytopathicity for distantly related lentiviruses that cause AIDS. Their conserved use implicates chemokine receptors as primordial lentivirus receptors. 相似文献