首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2265篇
  免费   0篇
综合类   1篇
化学工业   22篇
金属工艺   4篇
能源动力   2篇
轻工业   21篇
石油天然气   1篇
无线电   13篇
一般工业技术   9篇
冶金工业   2186篇
自动化技术   6篇
  2021年   4篇
  2019年   1篇
  2018年   3篇
  2017年   1篇
  2016年   4篇
  2013年   3篇
  2011年   2篇
  2010年   1篇
  2009年   1篇
  2008年   1篇
  2007年   4篇
  2006年   4篇
  2005年   3篇
  2004年   1篇
  2003年   5篇
  2002年   3篇
  2000年   2篇
  1999年   79篇
  1998年   648篇
  1997年   402篇
  1996年   226篇
  1995年   139篇
  1994年   117篇
  1993年   125篇
  1992年   35篇
  1991年   43篇
  1990年   29篇
  1989年   38篇
  1988年   31篇
  1987年   30篇
  1986年   17篇
  1985年   20篇
  1984年   2篇
  1983年   8篇
  1982年   10篇
  1981年   11篇
  1980年   19篇
  1979年   1篇
  1978年   8篇
  1977年   61篇
  1976年   112篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   4篇
  1969年   1篇
  1968年   1篇
  1964年   1篇
  1955年   1篇
排序方式: 共有2265条查询结果,搜索用时 93 毫秒
51.
PURPOSE: To evaluate in a prospective study the efficacy of autologous bone marrow transplantation (BMT) in adult patients with acute myelogenous leukemia (AML) in first remission, using a single course of high-dose Cytarabine (HD Ara-C) consolidation therapy as in vivo purging. PATIENTS AND METHODS: Sixty consecutive adult patients with AML in first complete remission (CR) were treated with HD Ara-C consolidation therapy as a method of in vivo purging before marrow collection. High-dose therapy consisted of fractionated total-body irradiation (FTBI) 12 Gy, intravenous etoposide 60 mg/kg, and cyclophosphamide 75 mg/kg, followed by reinfusion of cryopreserved marrow. RESULTS: Sixty patients underwent consolidation treatment with HD Ara-C with the intent to treat with autologous BMT. Sixteen patients were unable to proceed to autologous BMT (10 patients relapsed, one died of sepsis, one developed cerebellar toxicity, two had inadequate blood counts, and two refused). Forty-four patients underwent autologous BMT and have a median follow-up time of 37 months (range, 14.7 to 68.7) for patients who are alive with no relapse. The cumulative probability of disease-free survival (DFS) at 24 months in the intent-to-treat group is 49% (95% confidence interval [CI], 37% to 62%) and in those who actually underwent autologous BMT is 61% (95% CI, 46% to 74%). The probability of relapse was 44% (95% CI, 31% to 58%) and 33% (95% CI, 20% to 49%) for the intent-to-treat and autologous BMT patients, respectively. CONCLUSION: This approach offers a relatively high DFS rate to adult patients with AML in first CR. The results of this study are similar to those achieved with allogeneic BMT.  相似文献   
52.
53.
Nanosized gold particles (27 +/− 3 nm) have been proven to be effective in ameliorating the symptoms of mycobacterial-, collagen- and pristane-induced arthritis in rat models. This contrasts with the drug sodium aurothiomalate that was only effective against mycobacterial-induced arthritis but not to the same extent as Au0. Gold in the traditional Indian Ayurvedic medicine,Swarna bhasma (gold ash), has been characterized as globular particles of gold with an average size of 56–57 nm.  相似文献   
54.
Investigations were carried out in a long term field experiment from 1976 to 1982, on a loamy sand soil to find out the fertilizer requirements of groundnut and wheat grown in fixed rotation. Application of 26 kgP/ha to wheat alone was found to be sufficient for both wheat and succeeding groundnut. Application of phosphorus to both wheat and groundnut did not result in extra beneficial effect over P application to wheat alone. However, application of 26 kg P/ha to groundnut alone was not sufficient for succeeding wheat. There was no response from K application (25 kg K/ha) in either of these two crops. Increasing the dose of N from 50–150 kg/ha to wheat significantly increased the grain yield of wheat but the pod yield of succeeding groundnut were markedly lowered. Response of wheat to 150 kg N/ha was more marked when P was also applied to wheat and response was less when P was applied to preceding groundnut alone. Zinc application at 6.25 kg/ha to wheat alone resulted in significant increase in grain yield of wheat and pod yield of succeeding groundnut.  相似文献   
55.
Blends of linear low density polyethylene (LLDPE) and polypropylene (PP) show diverse mechanical property behavior in the published literature. The main objectives of this work were: to investigate the effect of viscosity of the component phases on the mechanical properties of such blends and to use the results to obtain a method for compatibilizing diaper manufacturing waste. The significant result of the study was that although LLDPE/PP blends are often termed “incompatible,” when viscosity of the components was more closely matched to each other, increases of as much as 50% in tensile strength and modulus were observed over the “rule of mixtures” line. Also, scanning electron microscopy then showed a more diffuse interface between the component phases. Three dimensional views of plots of viscosity ratio of the blend components as a function of temperature and shear rate were used to demonstrate the closer matching of viscosities for the blend components of the higher performing blends. In processing diaper manufacturing waste, addition of a high molecular weight PP in a manufacturing scale single screw extruder, to provide a closer match of viscosities of the blend components, significantly improved mechanical properties.  相似文献   
56.
57.
OBJECTIVES: This study assessed the incremental prognostic implications of normal and equivocal exercise technetium-99m (Tc-99m) sestamibi single-photon emission computed tomography (SPECT) and sought to determine its incremental prognostic value, impact on patient management and cost implications. BACKGROUND: The prognostic implications of Tc-99m sestamibi SPECT are not well defined, and risk stratification using this test has not been explored. METHODS: We studied 1,702 patients referred for exercise Tc-99m sestamibi SPECT who were followed up for a mean (+/- SD) of 20 +/- 5 months. Patients with previous percutaneous transluminal coronary angioplasty or coronary artery bypass surgery were excluded. The SPECT studies were assessed using semiquantitative visual analysis. Cardiac death and myocardial infarction were considered "hard" events, and coronary angioplasty and bypass surgery > 60 days after testing were considered "soft" events. RESULTS: Of the 1,702 patients studied, 1,131 had normal or equivocal scan results. A total of 10 events occurred in this group (1 cardiac death and 1 myocardial infarction [0.2% hard events]; 4 coronary angioplasty and 4 bypass surgery procedures [0.7% soft events]). The rates of hard events and referral to catheterization after SPECT were similarly low in patients with a low (< 0.15), intermediate (0.15 to 0.85) and high (> 0.85) post-exercise treadmill test (ETT) likelihood of coronary artery disease. With respect to scan type, patients with normal, probably normal or equivocal scan results had similarly low hard event rates. In the 571 patients with abnormal scan results, there were 43 hard events (7.5%) and 42 soft events (7.4%) (p < 0.001 vs. 1,131 patients with normal scan results for both). When the complete spectrum of scan responses was considered, SPECT provided incremental prognostic value in all patient subgroups analyzed. However, the nuclear scan was cost-effective only in patients with interpretable exercise ECG responses and an intermediate to high post-ETT likelihood of coronary artery disease and in those with uninterpretable exercise ECG responses and an intermediate to high pre-ETT likelihood of coronary artery disease. CONCLUSIONS: Normal or equivocal exercise Tc-99m sestamibi study results are associated with a benign prognosis, even in patients with a high likelihood of coronary artery disease. Although incremental prognostic value is added by nuclear testing in all patient subgroups, a testing strategy incorporating nuclear testing proved to be cost-effective only in the groups with an intermediate to high likelihood of coronary artery disease before scanning.  相似文献   
58.
Time-resolved absorption difference spectra of membrane suspensions of bovine rhodopsin at pH 5, 6, 7, 8, 9, and 10 were collected in the time range from 1 micro s to 200 ms after laser photolysis with 7-ns pulses of 477-nm light. The data were analyzed using singular value decomposition (SVD) and global exponential fitting. At pH 7 the data agree well with previously obtained data (Thorgeirsson et al. (1993) Biochemistry 32, 13861-13872) with fits improved at all pH's by inclusion of a small component due to an absorbance change caused by rotational diffusion which is detectable even at magic angle polarization. A "square scheme" suggested to best explain the previous data, which involves two branches following decay of the lumi intermediate with pathways (1) lumi --> MI480 right harpoon over left harpoon MII and (2) lumi right harpoon over left harpoon MI380 --> MII, could be confirmed throughout the entire pH range. However, to account for the increased rate of the MII --> MI480 reaction in path 1 for rising pH values, we propose that the MII in the square scheme consists of deprotonated MII and protonated MIIH+ forms in rapid equilibrium with each other, resulting in an extended square scheme and increasing the number of 380-nm products from two to three. In addition to the kinetic processes described by the extended square scheme, above pH 8 fast ( approximately 10 micro s) and slow ( approximately 50 ms) components were found. The fast component was assigned to the decay of a blue-shifted lumi intermediate, and the slow component, resolvable only at pH 10, was assigned to formation of a 450 nm absorbing photoproduct.  相似文献   
59.
In apparent contrast to earlier work on Epstein-Barr virus (EBV) carriage in the general Caucasian population, in vitro virus isolations from human immunodeficiency virus (HIV)-positive male homosexual cohorts have shown frequent examples of multiple EBV infection and an overall prevalence of type 2 EBV strains exceeding 30%. Here we ask to what extent these findings might hold true in another T-cell-immunocompromised cohort, HIV-positive hemophilic patients. Resident EBV strains were rescued within lymphoblastoid cell lines derived from the blood and throat washings of 39 such individuals, using the same in vitro protocols of virus isolation as for the homosexual cohort. A mean of 19 independent cell lines was made per patient, and in each case the resident virus was characterized by PCR-based viral genomic analysis and by immunoblotting to reveal the viral "EBNAprint." By these criteria a significant proportion (14 of 39) of the hemophilic cohort carried more than one EBV strain, suggesting that T-cell impairment does indeed sensitize virus carriers to reinfection with new strains of exogenously transmitted virus. However, the overall incidence of type 2 EBV infection was 10%, which is close to that observed in the earlier work with healthy carriers and substantially lower than that seen in HIV-positive homosexuals. We infer that type 2 EBV is relatively rare in the general Caucasian population but has become endemic in the homosexual community.  相似文献   
60.
BACKGROUND: Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem [123I] beta-CIT SPECT and platelet [3H]paroxetine binding. METHODS: Drug-free depressed and healthy subjects were injected with 211 +/- 22 MBq [123I] beta-CIT and imaged 24 +/- 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V3" = (brainstem-occipital)/occipital), a measure proportional to the binding potential (Bmax/Kd), was used for all comparisons. RESULTS: Results showed a statistically significant reduction in brainstem V3" values in depressed as compared to healthy subjects (3.1 +/- .9 vs. 3.8 +/- .8, p = .02). Platelet [3H]paroxetine binding was not altered (Bmax = 2389 +/- 484 vs. 2415 +/- 538 fmol/mg protein, p = .91) and was not significantly correlated with brainstem [123I] beta-CIT binding (r = -0.14, p = .48). CONCLUSIONS: These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号