全文获取类型
收费全文 | 2537篇 |
免费 | 25篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 16篇 |
综合类 | 13篇 |
化学工业 | 316篇 |
金属工艺 | 19篇 |
机械仪表 | 39篇 |
建筑科学 | 36篇 |
矿业工程 | 12篇 |
能源动力 | 38篇 |
轻工业 | 109篇 |
水利工程 | 17篇 |
石油天然气 | 6篇 |
无线电 | 102篇 |
一般工业技术 | 204篇 |
冶金工业 | 1459篇 |
原子能技术 | 17篇 |
自动化技术 | 166篇 |
出版年
2022年 | 12篇 |
2021年 | 8篇 |
2018年 | 15篇 |
2017年 | 15篇 |
2016年 | 6篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 60篇 |
2012年 | 39篇 |
2011年 | 59篇 |
2010年 | 47篇 |
2009年 | 65篇 |
2008年 | 71篇 |
2007年 | 48篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 32篇 |
2003年 | 32篇 |
2002年 | 43篇 |
2001年 | 35篇 |
2000年 | 22篇 |
1999年 | 61篇 |
1998年 | 317篇 |
1997年 | 208篇 |
1996年 | 156篇 |
1995年 | 100篇 |
1994年 | 92篇 |
1993年 | 109篇 |
1992年 | 39篇 |
1991年 | 43篇 |
1990年 | 52篇 |
1989年 | 58篇 |
1988年 | 58篇 |
1987年 | 39篇 |
1986年 | 38篇 |
1985年 | 36篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 30篇 |
1981年 | 42篇 |
1980年 | 24篇 |
1979年 | 11篇 |
1978年 | 21篇 |
1977年 | 52篇 |
1976年 | 114篇 |
1975年 | 14篇 |
1974年 | 13篇 |
1973年 | 16篇 |
1972年 | 8篇 |
1971年 | 8篇 |
排序方式: 共有2569条查询结果,搜索用时 171 毫秒
1.
IC Wilson TJ Gardner JM DiNatale AM Gillinov WE Curtis DE Cameron 《Canadian Metallurgical Quarterly》1993,106(5):805-810
Leukocyte depletion improves early postischemic ventricular performance in neonatal models of global myocardial ischemia. However, the rate of leukocyte reaccumulation after cardiopulmonary bypass and its subsequent impact on myocardial function is not known. This laboratory study examined the effect of leukocyte depletion on myocardial performance during the initial 6-hour period after bypass in an in situ, in vivo porcine model of neonatal cardiac surgery. Fifteen 3- to 5-day-old piglets (eight control and seven leukocyte depleted animals) were instrumented by placement of left ventricular short-axis sonomicrometry crystals and an intraventricular micromanometer catheter. Mechanical leukocyte depletion was achieved with Pall RC100 filters (Pall Biomedical, Inc., Fajardo, Puerto Rico) in the cardiopulmonary bypass circuit. Neonatal hearts were subjected to 90 minutes of hypothermic ischemia after a single dose of cold crystalloid cardioplegia. Two control animals died after the operation and were excluded from data analysis. Leukocyte filtration reduced the granulocyte count during initial myocardial reperfusion to 0.8% of control values. However, circulating granulocyte counts increased in leukocyte depleted animals throughout the postoperative period, reaching 68% of control values by 6 hours. Despite this rapid return of circulating granulocytes, animals subjected to leukocyte depletion had significantly better preservation of left ventricular performance (measured by preload recruitable stroke work, p < or = 0.02), left ventricular systolic function (measured by end-systolic pressure-volume relationship, p < or = 0.05), and ventricular compliance (p < or = 0.04) during the experiment. These changes in ventricular function were associated with a significant increase in left ventricular water content (p < or = 0.02) and tissue myeloperoxidase activity (p < or = 0.005) in control animals compared with leukocyte depleted animals. This study demonstrates that leukocyte depletion during initial reperfusion results in sustained improvement in postischemic left ventricular function despite the rapid return of granulocytes to the circulation. 相似文献
2.
3.
Assuming that the chemical reactions used to synthesize a combinatorial library member are successful, then knowledge of the specific reaction sequence is equivalent to knowing the member's chemical identity. Because the determination of chemical identity is typically not automatable and requires a substantial amount of material, schemes that encode a member's reaction history onto the reaction platform are of value. The primary benefits of encoding are relational nomenclature (all methods) and automated handling (some methods). Encoding methods evaluated to date are spatial, graphical, chemical, spectrometric, electronic, and physical. 相似文献
4.
The effects of circuit weight training on mood, perceived stress, job satisfaction, and physical symptoms were investigated in a sample of state law enforcement officers. 43 male officers who were not regularly exercising were assigned to either 4 mo of circuit weight training or a wait-list control condition. Four months of circuit weight training led to a significant increase in strength on cardiovascular fitness. Ss also demonstrated significant improvements in mood, including decreases in somatization, anxiety, depression, and hostility. Circuit weight training also resulted in a decrease in reports of physical symptoms and in improvements in job satisfaction. Results indicate that Ss who dropped out of the exercise training program evidenced significantly greater anxiety, depression, and hostility at pretreatment than Ss who completed the program. These findings suggest that circuit weight training programs may contribute to important psychological benefits. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
6.
7.
Hadjem A. Lautru D. Dale C. Man Fai Wong Hanna V.F. Wiart J. 《Microwave Theory and Techniques》2005,53(1):4-11
This paper gives a first comparison of specific absorption rate (SAR) induced in a child-sized (CS) head and an adult head using a dual-band mobile phone. In the second study, the visible human head is considered and comparison of SAR induced in a CS or child-like (CL) head and an adult head using a dual-band mobile phone is given. All the peaks of average SAR over a mass of 10 and 1 g in the head and the power budget are determined in the two comparisons using the finite-difference time-domain method. The differences between the results for adult and CS or CL heads are given at 900 and 1800 MHz. No important differences are noted for the peak SAR averaged over 10 g (SAR10 g), between the two adult head models, as well as between the two child head models. The peak SAR10 g in the brain of the CS or CL head is slightly more significant than that for the adult one. 相似文献
8.
Although accepted surgical techniques for peripheral nerve repair remain largely unchanged over the past three decades, much progress has been made toward understanding the mechanisms involved in nerve regeneration, and consequently toward providing adjunctive measures to enhance this regenerative process. We present a comprehensive review of the significant advances made in several aspects of nerve repair over the past decade, and particularly the past few years, and provide a few examples of facial nerve repair using the standard neurorrhaphy techniques recommended today. Several conclusions were drawn after thorough review of the literature. Early repair of injured nerves is preferred, and there appears to be no benefit to waiting for 3 weeks. Severed nerves should be repaired with monofilament 9-0 nylon suture placed in epineurial fashion. Fibrin glue confers no benefit in reattaching injured nerves. Likewise, theoretical advantages of laser neurorrhaphy have not resulted in improved nerve regeneration. Finally, trophic factors, such as apolipoproteins and nerve growth factor, and tubulization both appear to offer promise for future experimental and clinical progress in nerve repair. However, further work must be done to prove their efficacy. 相似文献
9.
PURPOSE: We attempted to evaluate the efficacy of transrectal bowel stimulation for neurogenic bowel dysfunction in children with myelodysplasia. MATERIALS AND METHODS: Daily sessions of transrectal electrostimulation were performed on an outpatient basis for 2 to 3 weeks on children with myelodysplasia and stool incontinence. If benefits were noted, 5 to 10 additional daily sessions were performed. Complete success was defined as improvement in all parameters of interest, including decrease in the frequency of daily bowel movements, increased sensation, increased ability to hold stool and a significant subjective change in bowel habits. Moderate success implied improvement in 1 to 3 parameters and treatment failure was defined as lack of improvement in any parameter. RESULTS: A total of 55 children 2 to 14 years old (mean age 6.7) completed a mean of 18 daily sessions per patient of bowel electrostimulation. Followup ranged from 1 to 6 years. Diapers are no longer required due to defecation problems in 14 children older than 3 years. Complete success was achieved in 20 cases (36.3%) and moderate success in an additional 30 (54.5%, overall success rate 90.8%). Specifically, 89% of the patients reported elimination of stooling accidents, 82% reported increased sensation and 71% were able to hold the bowel movement. Overall 68% of the patients noticed significantly improved bowel function. Complete/moderate success of transrectal electro-stimulation was statistically significant for all 4 parameters (p < 0.05), and complete success was significant for increased sensation, ability to hold and episodes of accidents. Therapy failed in 5 children (9%). There were no untoward effects. CONCLUSIONS: Transrectal electrostimulation is a well tolerated and minimally invasive modality that provides sustainable improvement in stool continence in children with myelomeningocele and neuropathic bowel dysfunction. 相似文献
10.
FM Loehrer CP Angst FP Brunner WE Haefeli B Fowler 《Canadian Metallurgical Quarterly》1998,13(3):656-661
BACKGROUND: Elevated homocysteine concentrations have been associated with premature arteriosclerosis and with impairment of key methylation reactions through accumulation of the homocysteine metabolite S-adenosylhomocysteine. In end-stage renal failure high homocysteine concentrations are commonly found but thus far the concentrations of related adenosylated metabolites in plasma have not been assessed. METHODS: In this prospective study we determined plasma homocysteine and related metabolites in 25 patients on regular haemodialysis, and in 40 healthy volunteers. Blood samples from patients were drawn immediately before and in 10 patients additionally after the dialysis session. RESULTS: Folic acid and vitamin B12 in plasma were similar in patients (mean +/- SEM 25+/-2 nmol/l and 400+/-41 pmol/l respectively) and controls (24+/-3 and 324+/-23 respectively). In patients plasma homocysteine, S-adenosylmethionine and S-adenosylhomocysteine were markedly elevated (36.6+/-3.6 micromol/l, 381+/-32nmol/l and 1074+/-55 nmol/l respectively) compared to the control values (6.8+/-0.4 micromol/l, 60+/-3 nmol/l and 24.4+/-1.1 nmol/l respectively) whereas the molar ratio of plasma S-adenosylmethionine and S-adenosylhomocysteine was significantly decreased (0.36+/-0.02 and 2.7+/-0.2 in patients and controls respectively). Haemodialysis failed to normalize the abnormal levels of these metabolites. CONCLUSION: Since the ratio of S-adenosylmethionine : S-adenosylhomocysteine is closely linked to the activity of numerous enzymatic methylation reactions, these results suggest that methylation may be impaired in these patients. 相似文献