全文获取类型
收费全文 | 198530篇 |
免费 | 2132篇 |
国内免费 | 633篇 |
学科分类
工业技术 | 201295篇 |
出版年
2021年 | 1252篇 |
2019年 | 1294篇 |
2018年 | 2130篇 |
2017年 | 2113篇 |
2016年 | 2177篇 |
2015年 | 1495篇 |
2014年 | 2626篇 |
2013年 | 7991篇 |
2012年 | 4475篇 |
2011年 | 6124篇 |
2010年 | 4941篇 |
2009年 | 5791篇 |
2008年 | 6173篇 |
2007年 | 6219篇 |
2006年 | 5649篇 |
2005年 | 5314篇 |
2004年 | 5261篇 |
2003年 | 5104篇 |
2002年 | 4909篇 |
2001年 | 5316篇 |
2000年 | 4928篇 |
1999年 | 5452篇 |
1998年 | 15685篇 |
1997年 | 10351篇 |
1996年 | 7944篇 |
1995年 | 5805篇 |
1994年 | 5034篇 |
1993年 | 5047篇 |
1992年 | 3399篇 |
1991年 | 3264篇 |
1990年 | 3227篇 |
1989年 | 3050篇 |
1988年 | 2801篇 |
1987年 | 2248篇 |
1986年 | 2316篇 |
1985年 | 2621篇 |
1984年 | 2323篇 |
1983年 | 2073篇 |
1982年 | 1906篇 |
1981年 | 2053篇 |
1980年 | 1791篇 |
1979年 | 1672篇 |
1978年 | 1661篇 |
1977年 | 2032篇 |
1976年 | 2710篇 |
1975年 | 1430篇 |
1974年 | 1379篇 |
1973年 | 1324篇 |
1972年 | 1133篇 |
1971年 | 958篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
E Gürdal-Yüksel M Karada? N Ozyardimci AE Kunt-Uzaslan T Yarkin 《Canadian Metallurgical Quarterly》1996,15(2-4):161-167
The purpose of our study was to evaluate the effects of cigarette smoking and serum lipids, folate, and vitamin B12 on the development of lung cancer in the Turkish population. The study group consisted of patients with histologically proven lung cancer and the control group comprised healthy smokers being followed in our smoking cessation outpatient department. Smoking history was obtained from all subjects and serum total cholesterol, HDL cholesterol, triglycerides, vitamin B12, and folate levels were measured. Pack/years of cigarettes smoked were significantly higher in the subjects with lung cancer than in the control group (p < 0.01). Serum total cholesterol, HDL cholesterol, triglyceride, serum folate, and vitamin B12 levels were within normal limits in both groups (p < 0.05), but serum vitamin B12 levels were statistically significantly higher (p < 0.01) in the cancer group than in the controls. In our study, we did not observe low levels of serum cholesterol, vitamin B12, or folate in the lung cancer patients. 相似文献
992.
T Yokoyama H Gondo Y Tanaka K Takenaka K Tanimoto M Nakamura Y Niho 《Canadian Metallurgical Quarterly》1996,37(4):358-361
A 62-year-old Japanese man complained of fever, general fatigue, anorexia and watery diarrhea during remission of adult T-cell leukemia-lymphoma. Laboratory examinations showed severe hypoproteinemia (2.9 g/dl). However, neither intestinal lesions associated with ATL nor findings suggesting protein losing gastroenteropathy were observed. Cytomegalovirus (CMV) antigen detection assay using peripheral blood leukocytes revealed that he had an active CMV infection with hemophagocytic syndrome. Treatment with ganciclovir and methylprednisolone led to an improvement of hypoproteinemia. CMV disease and associated hemophagocytic syndrome should be considered as a cause of hypoproteinemia in an immunocompromised host. 相似文献
993.
994.
E Asakura T Hanamura A Umemura K Yada T Yamauchi T Tanabe 《Canadian Metallurgical Quarterly》1996,195(3):300-313
M-CSF is a macrophage-lineage-specific growth factor that causes proliferation and differentiation of progenitor cells in the bone marrow. To investigate the effects of M-CSF on more matured cells, human monocytes were cultured in the presence or absence of M-CSF for 6 days. Addition of M-CSF at more than 10(2) U/ml resulted in higher viability and caused morphological differentiation to large macrophage-like cells. LPS-induced mediator production was also compared between M-CSF-treated and control cell. Monocytes were incubated with or without M-CSF for 3 days, and were stimulated with 1 microgram/ml of LPS for 2 days. IL-1 beta was not detected in the both culture supernatants, and PGE2 production was not influenced by M-CSF. However, amounts of G-CSF, GM-CSF, IL-6, and TNF-alpha produced in response to 1 microgram/ml of LPS were 1.5 to 2 times greater from monocytes treated with 10(4) U/ml of M-CSF than from control cells. The priming effect of M-CSF on LPS-induced cytokine production was found to require 3-day preincubation, and reached a maximum at the concentration of 10(4) U/ml. M-CSF-treated cells responded to a 10 times lower concentration of LPS than control cells in terms of cytokine production. M-CSF was also shown by flowcytometric analysis to influence the expression of CD14, a receptor for LPS, which might render monocytes more sensitive to LPS. 相似文献
995.
The problem of detonation-wave structure is studied on the basis of a mathematical model for the detonation of aluminum particles in oxygen within the framework of a single-velocity two-temperature continuum. An analysis of flow types in the form of the Chapman-Jouguet strong-detonation and weak-detonation regimes is given. A chart of the mixture flow regimes in the plane of the Mach number of the detonation wave and the ratio of the characteristic times of thermal relaxation and combustion is constructed using the results of numerical experiments. The domain of realization of only strong detonation regimes, the manifold of existence of weak and strong detonation regimes, and the domain of nonexistence of stationary solutions are determined. The structural properties of the solutions with an internal singular point and weak structurally unstable regimes with a saddle singularity in the final state are described. The stability of all types of stationary regimes against small and finite perturbations that retain the detonation-wave (DW) velocity and the final state is shown by numerical modeling of nonstationary detonation flows.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 2, pp. 74–85, March–April, 1996. 相似文献
996.
S Ikezaki A Nishikawa F Furukawa T Imazawa M Mitsui T Enami M Takahashi 《Canadian Metallurgical Quarterly》1995,(113):44-50
A 13-week subchronic toxicity study of josamycin was performed in male and female F344 rats to determine the maximum tolerable dose (MTD) for subsequent investigation of the carcinogenicity. As animals refused to take diet containing 5.0% josamycin in our preliminary study, dose levels in the present study were determined as 0, 0.16, 0.32, 0.63, 125 and 2.5% in diet. Rats were randomly allocated to 6 groups, each consisting of 10 males and 10 females. No animal died during the administration period and no group showed significant changes in body weight gain. Definite toxicity of josamycin was not noted in hematological and serum biochemical examinations. Histopathological examinations revealed no particular findings related to josamycin administration except cecal enlargement in the 1.25 and 2.5% groups. based on the results of the present study, it was concluded that the MTD of josamycin in 2.5% in diet, because the dietary dose level of 2.5% proved to exert no significant toxicological signs. 相似文献
997.
W.A. Baeslack III T.F. Broderick M. Juhas H.L. Fraser 《Materials Characterization》1994,33(4):357-367
Dissimilar-alloy welds have been produced between Ti---6Al---2Sn---Z4---2Mo---0.1Si (wt. %) and Ti---13.5Al---21.5 NB (wt.%) titanium aluminde using the three different solid-phase welding processes that create significantly different thermo-mechanical conditions at the weld interface. Exposure to supertransus temperatures, appreciable deformation and rapid cooling of the weld interface region during linear-friction welding promote dynamic recrystallization of beta grains and beta decomposition to fine martensitic products. In contrast, diffusion welding at temperatures below the base metal beta transus temperatures and at relatively low pressures minimizes deformation and microstructural variations in the weld interface region relative to the unaffected base metal. During capacitor-discharge resistance spot welding, extremely rapid heating of the weld interface region to near-solidus temperatures, and subsequent rapid cooling, result in the formation of a metastable, ordered-beta microstructure in the Ti---s13.5Al---21.6Nb and fine alpha-prime martensite in the Ti---6Al---2Sn---4Zr---2Mo-0.1Si. 相似文献
998.
Translated from Steklo i Keramika, No. 2, pp. 13–16, February, 1994. 相似文献
999.
J Norris L Harnack S Carmichael T Pouane P Wakimoto G Block 《Canadian Metallurgical Quarterly》1997,87(5):740-746
OBJECTIVES: This study examined US trends in nutrient intake, using almost identical methods and nutrient databases in two time periods. METHODS: An extensive dietary intake questionnaire was included in supplements to the 1987 and 1992 National Health Interview Surveys. Dietary data from approximately 11,000 persons in each of those years were analyzed. RESULTS: The total and saturated fat intake and the percentage of energy from fat declined among Whites and Hispanics, but only minimal changes were seen in Black Americans. The changes in fat intake were attributable principally to behavioral changes in frequency and type of fat-containing foods consumed rather than to the increased availability of leaner cuts of meat. Dietary cholesterol showed one of the largest declines of the nutrients examined. Less desirable changes were also seen. Cereal fortification played an important role in the observed changes in several micronutrients. CONCLUSIONS: Educational campaigns on dietary fat and cholesterol have been moderately effective, but not in all racial/ethnic groups. Future campaigns should emphasize maintaining or increasing micronutrient intake. 相似文献
1000.
Recent advances in control systems analysis and design have implied new uses for the Lyapunov equation of the form AX +XA T+Q =0. Implementation requirements for the incorporation of the use of Lyapunov equations in practical design, however, point out the need for a set of specialized numerical procedures. This special set of numerical procedures must efficiently solve large, sparse Lyapunov equations, solve sets of Lyapunov equations that differ only in the coefficient matrix Q , and provide good low rank estimates of the Lyapunov equation solution X in the case where low rank approximations are applicable. Discussions of the motivations for the solution of these problems and of candidate solution approaches are provided 相似文献