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   1151篇
  免费   15篇
  国内免费   3篇
电工技术   6篇
化学工业   122篇
金属工艺   14篇
机械仪表   12篇
建筑科学   11篇
能源动力   11篇
轻工业   28篇
水利工程   2篇
石油天然气   3篇
无线电   80篇
一般工业技术   62篇
冶金工业   767篇
原子能技术   4篇
自动化技术   47篇
  2023年   3篇
  2022年   10篇
  2021年   10篇
  2020年   10篇
  2019年   6篇
  2018年   15篇
  2017年   6篇
  2016年   11篇
  2015年   11篇
  2014年   14篇
  2013年   21篇
  2012年   14篇
  2011年   23篇
  2010年   12篇
  2009年   15篇
  2008年   13篇
  2007年   12篇
  2006年   13篇
  2005年   9篇
  2004年   6篇
  2003年   12篇
  2002年   12篇
  2001年   8篇
  2000年   6篇
  1999年   36篇
  1998年   267篇
  1997年   131篇
  1996年   89篇
  1995年   55篇
  1994年   47篇
  1993年   40篇
  1992年   12篇
  1991年   17篇
  1990年   19篇
  1989年   16篇
  1988年   22篇
  1987年   20篇
  1986年   13篇
  1985年   17篇
  1984年   8篇
  1983年   6篇
  1982年   4篇
  1981年   4篇
  1980年   6篇
  1979年   5篇
  1978年   2篇
  1977年   14篇
  1976年   34篇
  1975年   6篇
  1974年   2篇
排序方式: 共有1169条查询结果,搜索用时 15 毫秒
21.
22.
BACKGROUND: Sulphidoleukotrienes (slt) are important mediators in allergic diseases that are synthesized after allergen-specific stimulation. OBJECTIVES: The aim of this study is to determine in vitro slt production after allergen-specific (Dermatophagoides pteronyssinus) stimulus of peripheral blood leucocytes and to observe whether histamine release in whole blood with the same allergen correlates with slt production. We also wanted to evaluate whether a correlation exists between the release of slt and histamine and other diagnostic procedures as well as various clinical situations. METHODS: We studied 62 patients sensitive to Dermatophagoides pteronyssinus (Der p), 30 atopic controls and 12 healthy donors. We determined slt production using the CAST-ELISA technique and histamine release using two concentrations of Der p extract (20 and 2 ng/mL). We also carried out quantification of specific and total IgE levels, skin tests and pulmonary function test on each patient. RESULTS: We observed a significantly increased slt release after in vitro stimulation with Der p. There was a significant difference in the slt release between controls and sensitive patients (P < 0.001) and between atopic controls and sensitive patients (P < 0.001). The data are similar to those obtained with histamine release. We noted a positive correlation (P < 0.001) between slt and histamine release (r = 0.71, at 2 ng/mL and r = 0.83 at 20 ng/mL). We also found a positive (P<0.001), although weak (r=0.4 with at 2ng/mL, and r = 0.34 with P = 0.003 at 20 ng/mL) correlation between slt release and specific IgE levels as well as between slt release and skin-test reactivity (r = 0.49 at 2 ng/mL and r = 0.45 at 20 ng/mL; P < 0.001). No significant correlation between slt release and asthma severity was observed, although a trend toward higher slt production in severe and moderate asthma was detected. We found a significant (P<0.001) but weak (r=-0.3) negative correlation between age and slt release. With respect to sex-related differences, we found significant differences (P < 0.05) in slt release between the sexes with a higher slt release in men than in women. CONCLUSION: We conclude that CAST-ELISA for quantification of slt production is a useful in vitro method for diagnosing sensitization to Der p. There also exists a close correlation between slt release and other parameters of allergic sensitization in vitro as well as in vivo.  相似文献   
23.
24.
Typhoid fever is often associated with abnormal liver biochemical tests, but severe hepatic involvement with a clinical feature of acute hepatitis is a rare complication. There have been more than 150 cases of salmonella hepatitis reported from both developed and developing countries. The documented incidence varies widely from less than 1% to 26% patients with enteric fever. The possible associated factors for development of salmonella hepatitis are virulence of the organisms, delayed treatment and poor general health of the patients. The pathogenesis of severe hepatic involvement in salmonella infection may be multifactorial and includes endotoxin, local inflammatory and/or host immune reactions. Clinical jaundice in salmonella hepatitis usually occurs within the first 2 weeks of the febrile illness. Hepatomegaly and moderate elevation of transaminase levels are common findings. Extreme hepatic dysfunction with hepatic encephalopathy is a rare coexisting complication in salmonella hepatitis. A positive culture for salmonella from blood or stool is essential to differentiate salmonella hepatitis from other causes of acute hepatitis. Hepatic pathology is characterized by the presence of typhoid nodules with marked hyperplasia of reticuloendothelial cells. The prognosis is usually good as salmonella hepatitis responds well to a specific antibiotic therapy and juandice resolves with clinical improvement. The clinical course can be severe with a mortality rate as high as 20%, particularly with delayed treatment or in patients with other complications of salmonella infection. As enteric fever is a common infection, the recognition of salmonella hepatitis is of clinical importance.  相似文献   
25.
Organofunctional silanes recently have emerged as outstanding, environmentally friendly corrosion protectors for metal substrates, compared with conventional chromate treatments. A simple immersion technique is typically used to coat the metal surface with silane films. However, the thickness and uniformity of the films are uncontrolled in this process. This paper proposes a new deposition technique for the silane films on the metal surface, i.e., by electrodeposition. Hydrolyzed silanes are water-soluble, ionized molecules, so they can be deposited on metals by electrodeposition. Various combinations of silane mixtures were tested at different voltages, pH values, bath concentrations, and exposure times on panels of alloy aluminum and mirror-polished ferro-plate. The surface structure was characterized by scanning electron microscopy (SEM) and ellipsometry. The resistance of the film to corrosion was investigated by direct current (DC) polarization and electrochemical impedance spectroscopy (EIS) techniques. Electrodeposition results in a more organized and uniform film with fewer pores, compared with immersed or dipped films. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appears on pp. 320–26 of the Proceedings.  相似文献   
26.
Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina.  相似文献   
27.
Context: Most of the active pharmaceutical ingredients (APIs) suffer from a drawback of poor aqueous solubility. In addition to the same, some APIs show poor tabletting behavior creating problems in formulation development. Crystal engineering can be an efficient tool in rectification of such problems associated with the APIs. Thus present work deals with crystallization of ibuprofen (a model drug) onto the surface of dicalcium phosphate (DCP) particles using different techniques.

Objective: The objective of the present work was to prepare ibuprofen-loaded DCP particles and further to analyze them for compressibility and dissolution behavior.

Materials and methods: Various crystallization techniques such as solvent evaporation (SE), melt crystallization (MC), melt sonocrystallization (MSC), antisolvent crystallization (AC), and antisolvent sonocrystallization (ASC) were screened for the preparation of ibuprofen-loaded DCP. Products obtained from different techniques were analyzed for physicochemical, micromeritic and compression properties.

Results and discussion: ASC technique was found to be suitable for preparing directly compressible ibuprofen-loaded DCP particles. The change in the crystal habit (needle to plate shape) of ibuprofen and its crystallization in miniscular form onto the surface of DCP particles showed significant improvement in the dissolution rate and compression properties of ibuprofen due to an increase in specific surface area when compared with ibuprofen crystallized by other techniques. Additionally, the tablets prepared from ASC powder did not require binder since ibuprofen acted as melt binder during compression.

Conclusion: Directly compressible ibuprofen-loaded DCP particles can serve as an alternative for conventional ibuprofen tablets prepared by wet granulation technique.  相似文献   

28.
Context: The conventional liquid ophthalmic delivery systems exhibit short pre-corneal residence time and the relative impermeability to the cornea which leads to poor ocular bioavailability.

Objective: The aim of this study was to apply quality by design (QbD) for development of dexamethasone sodium phosphate (DSP) and tobramycin sulfate (TS)-loaded thermoresponsive ophthalmic in situ gel containing Poloxamer 407 and hydroxyl propyl methyl cellulose (HPMC) K4M for prolonging the pre-corneal residence time, ocular bioavability and decreases the frequency of administration of dosage form. The material attributes and the critical quality attributes (CQA) of the in situ gel were identified. Central composite design (CCD) was adopted to optimize the formulation.

Materials and methods: The ophthalmic in situ forming gels were prepared by cold method. Materials attributes were the amount of Poloxamer 407 and HPMC and CQA identified were Gel strength, mucoadhesive index, gelation temperature and % of drug release of both drug.

Results and discussion: Optimized batch (F*) containing 16.75% poloxamer 407 and 0.54% HPMC K4M were exhibited all results in acceptable limits. Compared with the marketed formulation, optimized in situ gel showed delayed Tmax, improved Cmax and AUC in rabbit aqueous humor, suggesting the sustained drug release and better corneal penetration and absorption.

Conclusion: According to the study, it could be concluded that DSP and TS would be successfully formulated as in situ gelling mucoadhesive system for the treatment of steroid responsive eye infections with the properties of sustained drug release, prolonged ocular retention and improved corneal penetration.  相似文献   

29.
Although Fetal Alcohol Syndrome (FAS) rates have been reported to be higher in American Indian populations, no screening tool has been validated for alcohol use in American Indian women. The objectives of this study were to compare the detection of prenatal alcohol use by a self-administered questionnaire to detection by clinical interview; and to ascertain whether the screening tool would increase detection of pregnant women who are abusing alcohol. The hospital records of the women were reviewed for any history of alcohol-related illnesses or injuries to compare with results obtained from the questionnaire. Seventy women attending their first prenatal clinic visit on a reservation were screened for alcohol use. There was a wide range in detection of prenatal alcohol use (20%-71% of the sample detected) depending on the method used. There was a large variation in sensitivities (7%-93%) of the individual questions in identifying patients detected as "high risk" by the clinicians. The T-ACE screening questions significantly increased detection of alcohol use compared to detection by the clinicians (p = 0.04 Fisher's exact test). Due to the large variation between different methods of detection, it is recommended that screening tools that increase detection of alcohol use should be combined with methods of higher specificity such as using questions about quantity and frequency of alcohol intake, medical chart review and clinical interview. We also found that various interpretations of the screening questions by the patients highlighted the need to tailor the wording of individual questions to the particular patient population.  相似文献   
30.
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