全文获取类型
收费全文 | 3847篇 |
免费 | 2篇 |
专业分类
综合类 | 3篇 |
化学工业 | 47篇 |
金属工艺 | 9篇 |
机械仪表 | 10篇 |
建筑科学 | 2篇 |
轻工业 | 14篇 |
水利工程 | 4篇 |
石油天然气 | 17篇 |
无线电 | 3篇 |
一般工业技术 | 54篇 |
冶金工业 | 3673篇 |
原子能技术 | 2篇 |
自动化技术 | 11篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 3篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 4篇 |
2012年 | 4篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2003年 | 8篇 |
2002年 | 2篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 131篇 |
1998年 | 1126篇 |
1997年 | 629篇 |
1996年 | 430篇 |
1995年 | 218篇 |
1994年 | 182篇 |
1993年 | 198篇 |
1992年 | 38篇 |
1991年 | 63篇 |
1990年 | 66篇 |
1989年 | 57篇 |
1988年 | 56篇 |
1987年 | 64篇 |
1986年 | 28篇 |
1985年 | 42篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 19篇 |
1981年 | 24篇 |
1980年 | 32篇 |
1979年 | 8篇 |
1978年 | 13篇 |
1977年 | 82篇 |
1976年 | 197篇 |
1975年 | 5篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1967年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有3849条查询结果,搜索用时 31 毫秒
971.
JS Fischgrund M Mackay HN Herkowitz R Brower DM Montgomery LT Kurz 《Canadian Metallurgical Quarterly》1997,22(24):2807-2812
STUDY DESIGN: This prospective study analyzed the influence of transpedicular instrumented on the operative treatment of patients with degenerative spondylolisthesis and spinal stenosis. OBJECTIVES: To determine whether the addition of transpedicular instrumented improves the clinical outcome and fusion rate of patients undergoing posterolateral fusion after decompression for spinal stenosis with concomitant degenerative spondylolisthesis. SUMMARY OF BACKGROUND DATA: Decompression is often necessary in the treatment of symptomatic patients who have degenerative spondylolisthesis and spinal stenosis. Results of recent studies demonstrated that outcomes are significantly improved if posterolateral arthrodesis is performed at the listhesed level. A meta-analysis of the literature concluded that adjunctive spinal instrumentation for this procedure can enhance the fusion rate, although the effect on clinical outcome remains uncertain. METHODS: Seventy-six patients who had symptomatic spinal stenosis associated with degenerative lumbar spondylolisthesis were prospectively studied. All patients underwent posterior decompression with concomitant posterolateral intertransverse process arthrodesis. The patients were randomized to a segmental transpedicular instrumented or noninstrumented group. RESULTS: Sixty-seven patients were available for a 2-year follow-up. Clinical outcome was excellent or good in 76% of the patients in whom instrumentation was placed and in 85% of those in whom no instrumentation was placed (P = 0.45). Successful arthrodesis occurred in 82% of the instrumented cases versus 45% of the noninstrumented cases (P = 0.0015). Overall, successful fusion did not influence patient outcome (P = 0.435). CONCLUSIONS: In patients undergoing single-level posterolateral fusion for degenerative spondylolisthesis with spinal stenosis, the use of pedicle screws may lead to a higher fusion rate, but clinical outcome shows no improvement in pain in the back and lower limbs. 相似文献
972.
The divergent commitment of ovarian granulosa cells to either proliferation and differentiation or programmed cell death directly reflects the process of follicular dominance and atresia. This process is regulated by FSH and local paracrine factors. To further analyze the role of FSH and intraovarian factors in follicular selection, we have established a rat ovarian granulosa (ROG) cell line from prepubertal (p14) rats. ROG cells are cultured in serum-free medium with activin A, but without FSH. ROG cells bind FSH and respond to FSH by a burst of cell proliferation and increased progesterone secretion. These results support the hypothesis that activin, but not FSH, is an important factor in the maintenance of immature granulosa cells. After exposure of ROG cells to FSH, withdrawal of FSH from the cultures results in apoptotic cell death. ROG cells start active membrane blebbing by 2 h after FSH withdrawal, and most cells die within 7 h. Thus, FSH-induced ROG cells differentiate into a more mature granulosa phenotype, which is nonmitotic and dependent on FSH for survival. The ROG cell line may thus provide a good in vitro model of follicular selection. 相似文献
973.
Unilateral naris closure in young rodents leads to striking alterations in the development of the ipsilateral olfactory system. One of the most pronounced effects is a 25% reduction in the size of the experimental olfactory bulb, a change that stems in part from decreased cell survival. Since naris occlusion in rodents alters the system more during development than in adulthood, we investigated the consequences of olfactory deprivation in a species that is born in a very immature state, Monodelphis domestica. In this pouchless marsupial, offspring are born after a short 14-day gestation. In the present study, the thymidine analogue bromodeoxyuridine was used to examine early postnatal neurogenesis in the olfactory bulb. Unlike rats and mice, neurogenesis of the main output neurons (the mitral cells) continues into postnatal life. Unilateral naris closure was begun on postnatal day 4 (P4) or P5 in Monodelphis and continued for 30 or 60 days. Laminar volume measurements revealed a significant reduction in the size of the experimental bulb following 60, but not 30, days of early olfactory deprivation. Mitral cell number estimates indicated a significant reduction after both 30 and 60 days of naris closure. The immaturity of Monodelphis offspring may render the population of mitral cells susceptible to the effects of olfactory deprivation. These findings suggest that afferent activity plays a role in the survival of all bulb neurons, irrespective of cell class. 相似文献
974.
There is a very strong need for an effective and reliable method of contraception in the diabetic woman. An unplanned pregnancy that occurs when her diabetes is not under good control can have disastrous consequences, ranging from abortion to a congenitally malformed fetus. The most important factor in the contraceptive decision for the diabetic patient, especially the IDDM patient, is that the choice be made not by the clinician alone or the patient alone, but through a carefully through-out process that involves both patient and physician. 相似文献
975.
CY Chan DC Molrine JH Antin C Wheeler EC Guinan HJ Weinstein NR Phillips C McGarigle S Harvey C Schnipper DM Ambrosino 《Canadian Metallurgical Quarterly》1997,20(1):33-38
OBJECTIVE: Although there are many anecdotal reports that psychological intervention is effective in enhancing adjustment to spinal cord injury (SCI), there are little data to support this assertion. To date, reports of few longitudinal-based controlled trials that assessed psychological outcomes for SCI persons have been published. This study was conducted to determine long-term efficacy of cognitive behavior therapy during rehabilitation. DESIGN: The study employed a nonrandomized controlled trial, and measures were taken on three occasions: before, immediately after, and 12 months after treatment. SETTING, OUTCOME MEASURES, AND INTERVENTION: Anxiety, depressive mood, and self-esteem were assessed in 28 SCI persons consecutively selected on admission to hospital, who participated in specialized group cognitive behavior therapy (CBT) during rehabilitation. CONTROLS: The intervention group's responses on the measures were compared with a control group of 41 SCI persons who only received traditional rehabilitation services during their hospitalization. RESULTS: There were no overall group differences on anxiety, depressive mood, and self-esteem, although there was a trend for the treatment group to have greater levels of improvement in depression scores across time in comparison to the control group. However, those in the treatment group who reported high levels of depressive mood before the CBT treatment were significantly less depressed 1 year after injury, compared to similar persons in the control group. CONCLUSIONS: While it appears not everyone who experiences SCI needs CBT, at least in the hospital phase of their rehabilitation, those who report high levels of depressive mood benefited greatly from CBT. 相似文献
976.
Chiropractic is an important component of the US health care system and the largest alternative medical profession. In this overview of chiropractic, we examine its history, theory, and development; its scientific evidence; and its approach to the art of medicine. Chiropractic's position in society is contradictory, and we reveal a complex dynamic of conflict and diversity. Internally, chiropractic has a dramatic legacy of strife and factionalism. Externally, it has defended itself from vigorous opposition by conventional medicine. Despite such tensions, chiropractors have maintained a unified profession with an uninterrupted commitment to clinical care. While the core chiropractic belief that the correction of spinal abnormality is a critical health care intervention is open to debate, chiropractic's most important contribution may have to do with the patient-physician relationship. 相似文献
977.
978.
LA Auersvald DM Rothstein SC Oliveira CQ Khuong H Onodera AI Lazarovits GP Basadonna 《Canadian Metallurgical Quarterly》1997,63(9):1355-1358
BACKGROUND: Although islet cell transplantation is considered an ideal form of endocrine replacement for type I diabetes, clinical application in humans is still not feasible. New immunosuppressive strategies are clearly needed to control inexorable rejection. CD45 is a family of transmembrane protein tyrosine phosphatases critically involved in the regulation of lymphocyte activation signals. Anti-CD45RB monoclonal antibody can prevent rejection of murine renal allografts. METHODS: Here, we examine the consequences of targeting CD45 in murine islet cell transplantation. Diabetic mice recipients received islet allografts under the kidney capsule and were divided into seven groups. Recipients received no treatment (controls) or anti-CD45RB monoclonal antibody (mAb; MB23G2 or C363.16A) at different dosages and treatment intervals. RESULTS: All untreated control animals lost islet function, becoming hyperglycemic within 10-17 days after transplantation. Animals treated with either anti-CD45RB mAb showed a significant prolongation of islet allograft survival when compared with controls. Anti-CD45RB MB23G2 at 100 microg/day, given on days -1, 0, and 5 was particularly effective, inducing indefinite islet allograft survival in 60% of recipients. CONCLUSIONS: These results indicate that anti-CD45 mAbs are potent immunomodulatory agents, able to sustain indefinite islet allograft function after a short treatment course in the highly immunogenic model of islet transplantation. 相似文献
979.
980.
We assessed relationships of evoked electrical and light scattering changes from cat dorsal hippocampus following Schaeffer collateral stimulation. Under anesthesia, eight stimulating electrodes were placed in the left hippocampal CA field and an optic probe, coupled to a photodiode or a charge-coupled device camera to detect scattered light changes, was lowered to the contralateral dorsal hippocampal surface. Light at 660 +/- 10 (SE) nm illuminated the tissue through optic fibers surrounding the optic probe. An attached bipolar electrode recorded evoked right hippocampal commissural potentials. Electrode recordings and photodiode output were simultaneously acquired at 2.4 kHz during single biphasic pulse stimuli 0.5 ms in duration with 0.1-Hz intervals. Camera images were digitized at 100 Hz. An average of 150 responses was calculated for each of six stimulating current levels. Stimuli elicited a complex population synaptic potential that lasted 100-200 ms depending on stimulus intensity and electrode position. Light scattering changes peaked 20 ms after stimuli and occurred simultaneously with population spikes. A long-lasting light scattering component peaked 100-500 ms after the stimulus, concurrently with larger population postsynaptic potentials. Optical signals occurred over a time course similar to that for electrical signals and increased with larger stimulation amplitude to a maximum, then decreased with further increases in stimulation current. Camera images revealed a topographic response pattern that paralleled the photodiode measurements and depended on stimulation electrode position. Light scattering changes accompanied fast electrical responses, occurred too rapidly for perfusion, and showed a stimulus intensity relationship not consistent with glial changes. 相似文献