全文获取类型
收费全文 | 83811篇 |
免费 | 1476篇 |
国内免费 | 966篇 |
专业分类
电工技术 | 1249篇 |
综合类 | 680篇 |
化学工业 | 10801篇 |
金属工艺 | 3648篇 |
机械仪表 | 2236篇 |
建筑科学 | 1678篇 |
矿业工程 | 540篇 |
能源动力 | 1811篇 |
轻工业 | 4243篇 |
水利工程 | 960篇 |
石油天然气 | 1434篇 |
武器工业 | 4篇 |
无线电 | 5768篇 |
一般工业技术 | 13934篇 |
冶金工业 | 28012篇 |
原子能技术 | 962篇 |
自动化技术 | 8293篇 |
出版年
2022年 | 329篇 |
2021年 | 440篇 |
2019年 | 418篇 |
2018年 | 1107篇 |
2017年 | 1321篇 |
2016年 | 1780篇 |
2015年 | 1307篇 |
2014年 | 1216篇 |
2013年 | 2777篇 |
2012年 | 3493篇 |
2011年 | 4253篇 |
2010年 | 2129篇 |
2009年 | 2511篇 |
2008年 | 2202篇 |
2007年 | 2373篇 |
2006年 | 1938篇 |
2005年 | 4539篇 |
2004年 | 3713篇 |
2003年 | 3100篇 |
2002年 | 1894篇 |
2001年 | 1845篇 |
2000年 | 1233篇 |
1999年 | 1601篇 |
1998年 | 8098篇 |
1997年 | 5313篇 |
1996年 | 3853篇 |
1995年 | 2385篇 |
1994年 | 1801篇 |
1993年 | 1837篇 |
1992年 | 832篇 |
1991年 | 870篇 |
1990年 | 818篇 |
1989年 | 753篇 |
1988年 | 655篇 |
1987年 | 618篇 |
1986年 | 557篇 |
1985年 | 543篇 |
1984年 | 371篇 |
1983年 | 378篇 |
1982年 | 422篇 |
1981年 | 462篇 |
1980年 | 529篇 |
1979年 | 399篇 |
1978年 | 389篇 |
1977年 | 1009篇 |
1976年 | 1899篇 |
1975年 | 401篇 |
1974年 | 330篇 |
1973年 | 355篇 |
1972年 | 313篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Soft tissue infections are among the rare manifestations of extra intestinal salmonellosis and occur more frequently in immunocompromised patients. Herein we report a case of a 51-year-old white male with type II. diabetes mellitus, diagnosed with supraclavicular abscess caused by Salmonella enteritidis. The patient denied any gastrointestinal symptoms, and stool cultures were negative. After incision, drainage, and administration of intravenous ampicillin (4 x 1.5 g/day for two weeks) the patient recovered completely. To our knowledge, this is the first reported case of cervical soft tissue abscess caused by Salmonella enteritidis without preceding gastrointestinal symptoms. We feel that the presence of diabetes was a risk factor for developing the infection. 相似文献
992.
Z Kelman A Yuzhakov J Andjelkovic M O'Donnell 《Canadian Metallurgical Quarterly》1998,17(8):2436-2449
Escherichia coli DNA polymerase III holoenzyme contains 10 different subunits which assort into three functional components: a core catalytic unit containing DNA polymerase activity, the beta sliding clamp that encircles DNA for processive replication, and a multisubunit clamp loader apparatus called gamma complex that uses ATP to assemble the beta clamp onto DNA. We examine here the function of the psi subunit of the gamma complex clamp loader. Omission of psi from the holoenzyme prevents contact with single-stranded DNA-binding protein (SSB) and lowers the efficiency of clamp loading and chain elongation under conditions of elevated salt. We also show that the product of a classic point mutant of SSB, SSB-113, lacks strong affinity for psi and is defective in promoting clamp loading and processive replication at elevated ionic strength. SSB-113 carries a single amino acid replacement at the penultimate residue of the C-terminus, indicating the C-terminus as a site of interaction with psi. Indeed, a peptide of the 15 C-terminal residues of SSB is sufficient to bind to psi. These results establish a role for the psi subunit in contacting SSB, thus enhancing the clamp loading and processivity of synthesis of the holoenzyme, presumably by helping to localize the holoenzyme to sites of SSB-coated ssDNA. 相似文献
993.
Hyperinsulinaemia, dyslipaemia and cardiovascular risk in girls with a history of premature pubarche
L Ibá?ez N Potau P Chacon C Pascual A Carrascosa 《Canadian Metallurgical Quarterly》1998,41(9):1057-1063
Girls with a history of premature pubarche, i.e. appearance of pubic hair before 8 years of age, show hyperinsulinism in response to an oral glucose tolerance test. As hyperinsulinaemia has a major role in dyslipaemia, and is considered an independent risk factor for cardiovascular disease, we assessed the patterns of plasma insulin concentration after a standard oral glucose tolerance test as well as fasting serum lipid, lipoprotein, and sex hormone-binding globulin concentrations in girls (n = 81) with premature pubarche compared with girls (n = 55) matched with them for stage and bone age to ascertain their metabolic states to identify those potentially at risk for the development of premature cardiovascular disease. Mean serum insulin concentrations were higher in patients at all pubertal stages, and associated with elevated serum triglyceride, very low density cholesterol and very low density triglyceride concentrations (p value range 0.04 to < 0.0001) but reduced sex hormone-binding globulin. Premature pubarche patients also displayed higher low density to high density lipoprotein cholesterol ratios compared with control subjects (p = 0.004 to 0.008). In conclusion, hyperinsulinaemia, decreased sex hormone-binding globulin concentrations and an unfavourable lipid pattern are common features in premature pubarche girls supporting the contention that atherogenic abnormalities composing the metabolic syndrome could start in childhood. To determine the clinical sequelae of such clustering of metabolic deviations, girls who were identified need to be followed up for the potential development of premature cardiovascular disease. 相似文献
994.
A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form. 相似文献
995.
996.
Horizontal-canal paroxysmal positional vertigo (HC-PPV) is a vestibular syndrome due to canalolithiasis of the horizontal canal. The more common posterior-canal paroxysmal positional vertigo has a well defined and effective therapy, while there have been few reports on physical therapy for HC-PPV, and these have been tried in relatively few patients. We report the results of two different types of treatment of HC-PPV in 92 patients. A group of 21 untreated patients acted as a control group. One method, known as forced prolonged position (FPP), proposes liberating the affected canal by gravitation, and involves having the patient lie on the healthy side for many hours. The other method (the barbecue rotation) is a liberatory manoeuvre which proposes to expel the otoconia from the canal by rotating the patient 270 degrees around the longitudinal axis of the body in rapid steps of 90 degrees. FPP was successful in more than 70% of our patients; the barbecue rotation had slightly less successful but more immediate results. Both methods enable otoconial debris to migrate into the posterior canal. We suggest treating all patients with the two methods in succession. 相似文献
997.
Low-back pain is a very common disease in Switzerland as elsewhere, with a prevalence of 65%. The pain is usually due to degeneration of the motion segment, but subsides spontaneously in some 95% of cases irrespective of the treatment. Only 5% of patients still have pain after one year; but account for over 80% of the costs due to low-back pain. Some patients can be helped by surgical fusion; however; preoperative identification of the pain source is mandatory. Since there is no consistent correlation between pain and the degree of degeneration of motion segments as seen on plain radiographs, functional radiographs, CT scan or MRI, other diagnostic methods such as facet blocks, discography and external diagnostic fixation must be used. After careful patient selection a fusion operation may be considered. Good results after fusion operations are reported in 60-80% of patients. The operative techniques are described. 相似文献
998.
Tannic acid, propyl gallate and methyl gallate, but not gallic acid, were found to be inhibitory to the growth of intestinal bacteria Bacteroides fragilis ATCC 25285, Clostridium clostridiiforme ATCC 25537, C. perfringens ATCC 13124, C. paraputrificum ATCC 25780, Escherichia coli ATCC 25922, Enterobacter cloacae ATCC 13047, Salmonella typhimurium TA98 and S. typhimurium YG1041 at 100-1000 microg/ml in culture broth. Neither Bifidobacterium infantis ATCC 15697 nor Lactobacillus acidophilus ATCC 4356 was inhibited by any of the above compounds up to 500 microg/ml. Tannic acid has a much greater relative binding efficiency to iron than propyl gallate, methyl gallate or gallic acid. The inhibitory effect of tannic acid to the growth of intestinal bacteria may be due to the strong iron binding capacity of tannic acid; whereas the effect of propyl gallate and methyl gallate probably occurs by a different mechanism. The growth of E. coli was restored by the addition of iron to the medium after the precipitate caused by tannic acid was removed. Neither B. infantis nor L. acidophilus require iron for growth. This probably contributes to their resistance to tannic acid. Because tannins are abundant in the human diet, tannins may affect the growth of some intestinal bacteria and thus may have an impact on human health. 相似文献
999.
OBJECTIVES: Sensory nerves play an important role in mediating neurogenic inflammation and subsequent tissue healing. A decrease in sensory nerve function with increasing age has been reported to correlate with poor tissue healing. Sympathetic nerves are known to modulate sensory nerve function, and changes in this modulation could also have important implications with ageing. The aims of this study were to examine the effect of different frequency electrical stimulation (ES) on the microvascular responses obtained to sensory nerve activation in young, aged and capsaicin-pretreated rats and modulation of these responses by sympathetic efferents. METHODS: Using laser Doppler flowmetry, vascular responses to antidromic ES of the sciatic nerve were monitored in the base of vacuum-induced blisters in the hind footpad. The non-selective alpha-adrenoceptor antagonist phentolamine (3 mg/kg, i.v.) was administered 20 min prior to ES. RESULTS: At high frequency ES (20V, 2ms, 15Hz for 1 min), the vascular response in old rats was significantly reduced (46 percent decrease, p < 0.05) compared to young control. At low frequency ES (20 V, 2 ms, 5 Hz for 1 min) however, older rats produced similar vascular responses to the young. Capsaicin-pretreated rats showed significantly reduced vascular responses to both high and low frequency ES, regardless of age. Pretreatment with phentolamine significantly increased the microvascular response in young rats at high (87 percent) and low (36 percent) frequency ES. In contrast, phentolamine significantly increased the ES-induced response in old rats at high frequency only (147 percent increase). CONCLUSIONS: The results suggest that the aged sensory nerve responds preferentially to low frequency ES and that sympathetic efferents exert an inhibitory modulatory effect on the vascular response evoked by sensory nerve stimulation. There are age-related changes in sympathetic modulation of sensory nerve-mediated responses which is dependent on stimulation frequency. 相似文献
1000.
JM Ramos-Fernández FM Oliete-García S Roldán-Aparicio E Kirchschl?ger A Barrio-Nicolás 《Canadian Metallurgical Quarterly》1998,26(153):752-755
INTRODUCTION: Sciatic nerve paralysis is a rare entity in the newborn. Few reference in specialized tests indicate that in the majority of cases the sciatic palsy has been observed after misplaced injections into the buttocks. The prognosis is variable and appears to be better after umbilical vessel catheterization for injection of medications than after misplaced muscular injections. In case of recovery it takes place within 3 to 12 months. OBJECTIVE: The objective of the present study is to know the evolution of neonatal sciatic palsy and to determine their injury noxe in regard to perinatal factors, and their relationship with long-time outcome, and to look for prognostic clues of clinical utility. MATERIAL AND METHODS: We evaluated perinatal factors of newborn children with sciatic nerve paralysis, followed for more than 18 months of clinical evolution, in a neuropediatric centre. RESULTS: Twenty one newborn with such criteria were evaluated. Gestational age was within 32 and 42 weeks (median 38.2). The birth weight was between 2,100 and 4,100 g (median 2,973). The majority of cases obtained total recovery (16 of 21). The time of recovery was 4 to 14 months (median 8.8). Free ambulation was obtained by all cases (at 10 to 24 months). No apparent cause was observed in the majority of cases. Cesarean delivery was more frequent specially in cases with permanent consequences. CONCLUSION: Long-time prognostic of neonatal sciatic palsy is generally good. In our series all the cases with consequences were associated to cesarean delivery. The duration of cesarean intervention and the anesthesic hypotony of the newborn could be implicated in the sciatic nerve injury of poor outcome. 相似文献