全文获取类型
收费全文 | 3297篇 |
免费 | 49篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 33篇 |
化学工业 | 323篇 |
金属工艺 | 31篇 |
机械仪表 | 22篇 |
建筑科学 | 39篇 |
矿业工程 | 2篇 |
能源动力 | 27篇 |
轻工业 | 250篇 |
水利工程 | 7篇 |
石油天然气 | 2篇 |
无线电 | 244篇 |
一般工业技术 | 363篇 |
冶金工业 | 1723篇 |
原子能技术 | 33篇 |
自动化技术 | 250篇 |
出版年
2022年 | 25篇 |
2021年 | 33篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 32篇 |
2017年 | 31篇 |
2016年 | 30篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 107篇 |
2012年 | 57篇 |
2011年 | 83篇 |
2010年 | 52篇 |
2009年 | 65篇 |
2008年 | 79篇 |
2007年 | 49篇 |
2006年 | 71篇 |
2005年 | 64篇 |
2004年 | 37篇 |
2003年 | 47篇 |
2002年 | 39篇 |
2001年 | 53篇 |
2000年 | 40篇 |
1999年 | 86篇 |
1998年 | 492篇 |
1997年 | 286篇 |
1996年 | 197篇 |
1995年 | 127篇 |
1994年 | 125篇 |
1993年 | 130篇 |
1992年 | 57篇 |
1991年 | 30篇 |
1990年 | 34篇 |
1989年 | 34篇 |
1988年 | 42篇 |
1987年 | 41篇 |
1986年 | 39篇 |
1985年 | 38篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 31篇 |
1981年 | 24篇 |
1980年 | 31篇 |
1978年 | 25篇 |
1977年 | 48篇 |
1976年 | 106篇 |
1975年 | 31篇 |
1973年 | 16篇 |
1972年 | 15篇 |
1970年 | 14篇 |
排序方式: 共有3349条查询结果,搜索用时 15 毫秒
31.
PURPOSE: Previous research has demonstrated that testosterone therapy causes a profound suppression of autoimmune disease in lacrimal glands of female mouse models of Sj?gren's syndrome. The aim of the present study was to determine whether other anabolic androgens, nonandrogenic steroids, or immunosuppressive agents might duplicate this hormonal effect. For comparative purposes, we also evaluated the influence of these various pharmacologic compounds on the tear volume, the magnitude of lymphocyte infiltration in the submandibular gland, and the extent of mucosal and peripheral lymphadenopathy. METHODS: Female MRL/MpJ-lpr/lpr mice were administered vehicle, steroids, or immunosuppressive compounds for 21 days after the onset of disease. Lacrimal glands and tears, as well as submandibular glands, spleens, and superior cervical and mesenteric lymph nodes were collected immediately before or after treatment and then processed for analysis. RESULTS: Our results showed that: (1) the immunosuppressive impact of testosterone on lymphocyte infiltration in lacrimal tissue was reproduced by the administration of 19-nortestosterone or cyclophosphamide, but not by therapy with 17 beta-estradiol, danazol, the experimental steroid Org 4094, cyclosporine A or dexamethasone; (2) treatment with testosterone, 19-nortestosterone, cyclophosphamide, or dexamethasone significantly reduced the extent of inflammation in salivary glands; (3) exposure to cyclophosphamide markedly diminished the size of lymphatic and splenic tissues, whereas glucocorticoid treatment only decreased the weight of superior cervical lymph nodes; and (4) administration of 17 beta-estradiol, Org 4094, or dexamethasone led to a significant decrease in tear volume. CONCLUSIONS: Overall, these results demonstrate that androgen or cyclophosphamide therapy may successfully ameliorate autoimmune expression in lacrimal and salivary glands of a female mouse model of Sj?gren's syndrome. 相似文献
32.
Quaternary ammonium salts of sulfonated polystyrene (SPS) were used as compatibilizers for melt intercalation of PS and pristine Na-montmorillonite. Tetra-octyl ammonium SPS and tetra-decyl ammonium SPS ionomeric compatibilizers produced significant exfoliation and a homogeneous dispersion of the polymer-clay nanocomposites. Wide angle X-ray diffraction and transmission electron microscopy were primarily used to characterize the morphology of the nanocomposites. Image analysis was used to measure the percentage exfoliation. Exfoliation increased with the increasing length of the alkyl chain of the ammonium counter-ion of the SPS ionomer. The nanocomposites containing ionomers exhibited higher storage moduli compared to nanocomposites without the compatibilizer. 相似文献
33.
The authors describe their perspectives as a psychologist married couple and discuss some of the major trends that have affected their work in the last years, including the women's movement and new developments in the field of psychology. They note both positive and negative changes from the last 2 decades. Whereas there are many more new and exciting opportunities for psychologists today, there are also more pressures, more stringent training and credentialing requirements, more competition, and less mobility. Also discussed are some advantages to being married to another psychologist, including understanding each other's roles, combining social and professional lives, and expanding professional networks. They look to the future of psychology with optimism and hope that by examining and changing some of the restrictions on psychologists today, the field of professional psychology can be made more rewarding for future psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
34.
35.
E.R. Weiss R.J. Braddock R.M. Goodrich J.F. Gregory III J. Pika 《Journal of food science》2003,68(6):2146-2149
ABSTRACT: Screening commercial cold-pressed oils revealed the presence of terpene chlorohydrins, which may have quality and safety implications for end-users. Concentrations of (1R, 2R, 4R)-2-chloro-8- p -menthen-1-ol in some citrus essential oils ranged from less than 1 to 140 ppm. More than half of the oils tested contained less than 2 ppm of (1R, 2R, 4R)-2-chloro-8- p -menthen-1-ol. A pilot plant study used different concentrations of chlorinated water during the oil-recovery process. Cold-pressed oil, produced from a 30-ppm chlorine solution, contained (1R, 2R, 4R)-2-chloro-8- p -menthen-1-ol at detection threshold. The presence of (1R, 2R, 4R)-2-chloro-8- p -menthen-1-ol in citrus essential oils results from processing conditions and can be reduced through the reduction of chlorine levels in treatment water. 相似文献
36.
In this paper we study the performance of direction-finding systems which attempt to estimate unknown array parameters (such as sensor gains and phases) in addition to the estimation of the directions of arrival (DOA), as a way of performing array self-calibration. We develop compact closed form expressions for the Cramér-Rao bound associated with the joint estimation of DOAs, gains, phases, and the signal covariance matrix. By evaluating the Cramér-Rao bound for selected cases we gain some insight into the performance of direction-finding systems in the presence of gain and phase uncertainties.This work was supported by the Army Research Office under Contract No. DAAL03-89-C-0007, sponsored by U.S. Army Communications Electronics Command, Center for Signals Warfare. 相似文献
37.
N Weiss V Gudnasson P Ostwald S Humphries H Schuster C Keller 《Canadian Metallurgical Quarterly》1997,13(3):141-151
The DNA adduct 8-hydroxy-2'-deoxyguanosine (8-OHdG) has been widely used as a biomarker for oxidative stress. Bulky DNA adducts, which are detectable by the 32P-postlabelling method, provide evidence for exposure to and metabolic activation of large, mainly apolar compounds, e.g. polycyclic aromatic hydrocarbons. We determined both types of adducts in placental tissues of 30 term pregnancies and related the adduct levels to the exposure to tobacco smoke and the plasma antioxidant status. Urine and plasma continine concentrations were used to select 10 nonsmokers, 9 nonsmokers exposed to environmental tobacco smoke (ETS) and 11 smoking women. Placental levels of 8-OHdG were 0.84 +/- 0.11, 0.90 +/- 0.21 and 0.83 +/- 0.20/10(5) deoxyguanosine bases (dG) for nonsmokers, nonsmokers exposed to ETS and smokers, respectively. The differences between the groups were not significant. Smoking women had significantly lower plasma vitamin C and beta-carotene concentrations than nonsmoking women or nonsmoking women exposed to environmental tobacco smoke. The 8-OHdG adduct level in placental DNA was inversely correlated with the plasma vitamin E concentration (r = -0.47, P < 0.05). There was no association between placental 8-OHdG adducts and vitamin A, C and beta-carotene in plasma. In total, 15 different adducts could be identified in the 30 placenta samples by the 32P-postlabelling method. There was a strong inter-individual variation in both the number of adducts and adduct intensities. No smoking-related or vitamin-related effects on adduct patterns or intensities were found. Our findings suggests that, within the limits of the methods used, tobacco smoke exposure during pregnancy does not lead to a measurable increase in placental DNA adduct levels and that vitamin E appears to have a protective effect on placental 8-OHdG formation. 相似文献
38.
K. Eschenroder H. Kiefhaber G. Weiss J. Classen 《Journal of Low Temperature Physics》1997,109(1-2):163-181
The property of solid hydrogen (H2, HD and D2) not to wet an attractive substrate, can be used to prepare micron sized hydrogen crystals. We used surface acoustic waves
(SAW) in the range from 100 MHz to 1 GHz to study the elastic properties of the crystallite-substrate system. The growth of
crystallites at temperatures around 3 K can be monitored by the resonant coupling of elastic eigenmodes to the SAW. We observed
drastic changes of the resonant coupling for all isotopes when the temperature was varied between 0.15 K and 2.4 K. Possible
origins of this unexpecied effect are discussed including a temperature variation of the wetting behavior. For H2 the impact of the ordering transition of ortho-H2 was also investigated. 相似文献
39.
OBJECTIVE: To study the utility and functional benefits of an implanted functional electrical stimulation (FES) system for hand grasp and release in adolescents with tetraplegia secondary to spinal cord injuries. DESIGN: Intervention study with before-after trial measurement with each subject as his or her own control. SETTING: Nonprofit pediatric orthopedic rehabilitation facility specializing in spinal cord injury. PARTICIPANTS: A convenience sample of five adolescents between 16 and 18 years of age with C5 or C6 level tetraplegia at least 1 year after traumatic spinal cord injury. Key muscles for palmar and lateral grasp and release were excitable by electrical stimulation. INTERVENTIONS: A multichannel stimulator/receiver and eight electrodes were surgically implanted to provide stimulated palmar and lateral grasp and release. In conjunction with implantation of the FES hand system, surgical reconstruction in the form of tendon transfers, tendon lengthenings and releases, and joint arthrodeses was performed to augment stimulated hand function. Rehabilitation of the tendon transfers and training in the use of the FES hand system were provided. MAIN OUTCOME MEASURES: Measurements of pinch and grasp force, the Grasp and Release Test (GRT), and an assessment of six activities of daily living (ADL) were administered before implantation of the FES hand system and at regular follow-up intervals. Results of the stimulated response of individual muscles and surgical reconstruction were evaluated using standard and stimulated muscle testing techniques and standard assessment of joint range of motion. All subjects completed followup testing. RESULTS: Lateral and palmar forces were significantly greater than baseline forces (p = .043). Heavy objects on the GRT could only be manipulated with FES, and FES increased the level of independence in 25 of 30 ADL comparisons (5 subjects, 6 activities) as compared to baseline. After training, FES was preferred in 21 of 30 comparisons over the typical means of task completion. Of the 40 electrodes implanted, 37 continue to provide excellent stimulated responses and all of the implanted stimulators have functioned without problems. The surgical reconstruction procedures greatly enhanced FES hand function by either expanding the workspace in which to utilize FES (deltoid to triceps transfer), stabilizing the wrist (brachioradialis to wrist extensor transfer), or stabilizing joints (intrinsic tenodesis transfer, FPL split transfer). CONCLUSION: For five adolescents with tetraplegia, the combination of FES and surgical reconstruction provided active palmar and lateral grasp and release. Laboratory-based assessments demonstrated that the FES system increased pinch force, improved the manipulation of objects, and typically increased independence in six standard ADL as compared to pre-FES hand function. The study also showed that the five adolescents generally preferred FES for most of the ADL tested. Data on the benefits of the implanted FES hand system outside of the laboratory are needed to understand the full potential of FES. 相似文献
40.
BD Weiss 《Canadian Metallurgical Quarterly》1994,13(1):175-186
Symptoms related to the bicycle seat are common among cyclists. Skin problems, such as chafing, ischial tuberosity pain, folliculitis, and ulceration are particularly common. Although rarely serious, these problems may cause significant discomfort and interfere with a cyclist's ability to ride. Numerous preventive measures have been recommended to prevent these problems, mostly related to seat position, seat construction, and bicycling pants. Little research is available, however, to support any of these recommendations. Research does indicate that use of skin creams is not effective for prevention of bicycle-related skin problems. 相似文献