全文获取类型
收费全文 | 1400篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 2篇 |
综合类 | 4篇 |
化学工业 | 23篇 |
金属工艺 | 4篇 |
机械仪表 | 9篇 |
建筑科学 | 7篇 |
能源动力 | 6篇 |
轻工业 | 27篇 |
水利工程 | 4篇 |
石油天然气 | 2篇 |
无线电 | 4篇 |
一般工业技术 | 13篇 |
冶金工业 | 1280篇 |
原子能技术 | 2篇 |
自动化技术 | 16篇 |
出版年
2021年 | 5篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2015年 | 2篇 |
2014年 | 6篇 |
2013年 | 8篇 |
2012年 | 4篇 |
2011年 | 6篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 5篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 33篇 |
1998年 | 417篇 |
1997年 | 214篇 |
1996年 | 152篇 |
1995年 | 70篇 |
1994年 | 65篇 |
1993年 | 75篇 |
1992年 | 7篇 |
1991年 | 19篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 10篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 13篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 39篇 |
1976年 | 84篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1958年 | 1篇 |
1928年 | 1篇 |
1909年 | 1篇 |
1885年 | 4篇 |
排序方式: 共有1403条查询结果,搜索用时 40 毫秒
41.
42.
Magnetic resonance images (MRIs) of the brains of 11 patients aged from 1 week to 12 years with a distinctive type of cerebral palsy were selected based on distribution of cerebral lesions, which were restricted to bilateral perirolandic cortical and subcortical regions, including frequent symmetric involvement of basal ganglia and ventrolateral nucleus of thalami. Retrospectively, the perinatal history and clinical features were reviewed to correlate clinical data with this distinctive pattern of brain injury. Clinically affected neonates had an encephalopathy associated with a severe perinatal asphyxial event. Older children with cerebral palsy survived a similar perinatal course and demonstrated spastic quadriparesis with bulbar or pseudobulbar involvement, lack of verbal speech and variable delays in cognitive development. The distribution of hypoxic-ischemic lesions involving bilateral perirolandic regions, basal ganglia, and thalami, appears to correlate with increased metabolic areas of primary myelination in full-term neonates, but not with arterial border zones nor a single cerebral artery distribution. Myelination is a critical process in maturing brain associated with marked increase in tissue respiration and thus greater susceptibility to oxygen deprivation. It is believed that the extent of hypoxic-ischemic brain injury is determined principally by brain maturity and regional metabolic rates at time of insult and this correlates with active myelination in full-term neonates. This study confirms previous data from neuropathologic literature and recent reports of neuroimaging studies of asphyxiated neonates. In addition, retrospective analysis of the clinical data enables recognition of a type of cerebral palsy that might be the hallmark of hypoxic-ischemic injury in term neonates. 相似文献
43.
LL Judd HS Akiskal JD Maser PJ Zeller J Endicott W Coryell MP Paulus JL Kunovac AC Leon TI Mueller JA Rice MB Keller 《Canadian Metallurgical Quarterly》1998,55(8):694-700
BACKGROUND: Investigations of unipolar major depressive disorder (MDD) have focused primarily on major depressive episode remission/recovery and relapse/recurrence. This is the first prospective, naturalistic, long-term study of the weekly symptomatic course of MDD. METHODS: The weekly depressive symptoms of 431 patients with MDD seeking treatment at 5 academic centers were divided into 4 levels of severity: (1) depressive symptoms at the threshold for MDD; (2) depressive symptoms at the threshold for minor depressive or dysthymic disorder (MinD); (3) subsyndromal or subthreshold depressive symptoms (SSDs), below the thresholds for MinD and MDD; and (4) no depressive symptoms. The percentage of weeks at each level, number of changes in symptom level, and medication status were analyzed overall and for 3 subgroups defined by mood disorder history. RESULTS: Patients were symptomatically ill in 59% of weeks. Symptom levels changed frequently (1.8/y), and 9 of 10 patients spent weeks at 3 or 4 different levels during follow-up. The MinD (27%) and SSD (17%) symptom levels were more common than the MDD (15%) symptom level. Patients with double depression and recurrent depression had more chronic symptoms than patients with their first lifetime major depressive episode (72% and 65%, respectively, vs 46% of follow-up weeks). CONCLUSION: The long-term weekly course of unipolar MDD is dominated by prolonged symptomatic chronicity. Combined MinD and SSD level symptoms were about 3 times more common (43%) than MDD level symptoms (15%). The symptomatic course is dynamic and changeable, and MDD, MinD, and SSD symptom levels commonly alternate over time in the same patients as a symptomatic continuum of illness activity of a single clinical disease. 相似文献
44.
45.
LL Siu G Attardo E Izbicka R Lawrence C Cerna L Gomez K Davidson C Finkle C Marsolais EK Rowinsky DD Von Hoff 《Canadian Metallurgical Quarterly》1998,9(8):885-891
BACKGROUND: BCH-4556 ((-)-2'-deoxy-3'-oxacytidine) is an L-nucleoside analogue shown to have broad preclinical anti-cancer activity, particularly against solid neoplasms such as prostate, renal, and hepatoma in vitro and in vivo, in contrast to cytosine arabinoside (ara-C) which is preferentially active against leukemia. MATERIALS AND METHODS: The antitumor activity of BCH-4556 was evaluated using human tumor colony-forming unit (HTCFU) assay, in which fresh tumor specimens were taken directly from patients with and without prior chemotherapy. RESULTS: Overall, in vitro responses (50% or less survival compared to untreated controls) were observed in 11% (two of 18), 29% (five of 17) and 50% (nine of 18) of specimens treated for one hour with BCH-4556 at 1, 10 and 100 micrograms/ml, respectively; and 16% (nine of 55), 32% (24 of 74), 48% (35 of 73) and 65% (11 of 17) of specimens treated continuously with BCH-4556 at 0.1, 1, 10 and 100 micrograms/ml, respectively. With the one-hour schedule, a significant difference in response rates was noted between 100 micrograms/ml and 1 microgram/ml (P = 0.02). With the continuous schedule, significant differences in response rates were observed between 1 microgram/ml and 0.1 microgram/ml (P = 0.02), between 10 micrograms/ml and 0.1 microgram/ml (P = 0.0001), as well as between 10 micrograms/ml and 1 microgram/ml (P = 0.01). A trend suggesting the superiority of continuous exposure was observed in paired specimens (n = 18) at comparable drug concentrations. Activity was noted against ovarian (nine of 16 = 56%), renal (three of four = 75%), and melanoma (two of two = 100%) HTCFU at 10 micrograms/ml using the continuous schedule. Comparisons between BCH-4556 and paclitaxel were made in 32 specimens at 10 micrograms/ml using the continuous exposure. Twenty-three specimens showed similar responses with both drugs; seven showed better responses with BCH-4556; and two showed better responses with paclitaxel (P = 0.18). CONCLUSIONS: Promising activity was observed with BCH-4556 against ovarian, renal, and melanoma HTCFU. There appeared to be a positive relationship between BCH-4556 concentration and response using both one-hour and continuous exposures. Continuous exposure to BCH-4556 provided high response rates especially at concentrations above 10 micrograms/ml. For both one-hour and continuous exposures, BCH-4556 had similar, and at times, greater potency than paclitaxel against the same tumor specimens in the present study. 相似文献
46.
A Bhandari DG Jones JR Schullek K Vo CA Schunk LL Tamanaha D Chen Z Yuan MC Needels MA Gallop 《Canadian Metallurgical Quarterly》1998,8(17):2303-2308
Phosphomannose Isomerase (PMI) has been shown by genetic methods to be an essential enzyme in fungal cell wall biosynthesis. The PMI inhibitor AF14049 was discovered as an unanticipated side product from high-throughput library screening against the enzyme from C, albicans. Solid-phase synthetic methods were developed and a series of libraries and discrete analogs synthesized to explore SAR around AF14049. 相似文献
47.
The effect of chronic in vivo glutathione (GSH) depletion by L-buthionine-[S,R]-sulfoximine (BSO) on intracellular and interorgan GSH regulation was investigated in mice both at rest and after an acute bout of exhaustive swim exercise. BSO treatment for 12 days decreased concentrations of GSH in the liver, kidney, quadriceps muscle, and plasma to 28, 15, 7, and 35%, respectively, compared to GSH-adequate mice. In most tissues, with the exception of the kidney, this decrease was associated with a concomitant decrease of glutathione disulfide (GSSG) such that the GSH/GSSG ratio was maintained. GSH depletion caused adaptive changes in several enzymes related to GSH regulation, such as liver glutathione peroxidase (-25%), kidney gamma-glutamyltranspeptidase (+20%), glutathione disulfide reductase (+131%) and glutathione sulfur-transferase (+53%). There was an apparent down-regulation of muscle gamma-glutamyltranspeptidase (-56%) in the GSH-depleted mice, which contributed to a conservation of plasma GSH. Exhaustive exercise in the GSH-adequate state severely depleted GSH content in the liver (-55%) and kidney (-35%), whereas plasma and muscle GSH levels remained constant. However, exercise in the GSH-depleted state exacerbated GSH deficit in the liver (-57%), kidney (-33%), plasma (-65%), and muscle (-25%) in the absence of adequate reserves of liver GSH. Hepatic lipid peroxidation increased by 220 and 290%, respectively, after exhaustive exercise in the GSH-adequate and -depleted mice. We conclude that GSH homeostasis is essential for the prooxidant-antioxidant balance during prolonged physical exercise. 相似文献
48.
The skeletal features of a moderately decomposed decapitated head recovered in 1993 are consistent with torticollis (wryneck) and inconsistent with other possible syndromes. Asymmetries of the face, cranial vault, mandible, and cervical vertebrae closely resemble published cases of paleopathological and recent torticollis. The laterally directed left occipital condyle and articulation of the basicranium and cervical vertebrae indicate that the head was tipped toward the left shoulder. Right-left asymmetries of areas of muscular attachments are compatible with a leftward head deviation. Mild arthritis of the atlantal-occipital and intervertebral joints, clinoid bridging, and thickening of the inner table of the frontal squamosa may not be related to the possible torticollis. The postural deviations of the head and neck may aid in the identification of this homicide victim, as did skeletal evidence to torticollis in an earlier case from Britain. 相似文献
49.
Protein shedding, or the proteolytic cleavage of a protein from the surface of a cell, is emerging as an important mechanism in the regulation of cellular activity but it is poorly understood. Growing evidence suggesting that protein shedding and protein function are closely linked may lead to new strategies for the treatment of a wide range of diseases. 相似文献
50.
LL Dever SM Smith D Dejesus M Masurekar D Patel ZC Kaminski WG Johanson 《Canadian Metallurgical Quarterly》1996,2(4):407-413
OBJECTIVE: Previous studies of surgical treatment for acromegaly have used varied criteria for 'cure', but elevated GH levels are considered to be associated with continuing disease activity. We wished to analyse the results of transsphenoidal pituitary surgery for acromegaly and assess the longer-term outcome for patients not offered further treatment when post-operative levels of GH < 5 mU/l were achieved. DESIGN: We studied a retrospective group of patients who underwent transsphenoidal surgery for acromegaly at St Bartholomew's Hospital between 1985 and 1993. PATIENTS: One hundred consecutive patients (53 male, mean age 46 years, range 18-68 years) undergoing transsphenoidal surgery for acromegaly were assessed. The patients were followed for a mean of 3.8 years (range 0.5-8 years) after operation. MEASUREMENTS: GH levels are represented as a mean value from a four-point day curve taken at 0830, 1300, 1700 and 1900 h. ACTH reserve was assessed basally and, if this was normal, with the insulin tolerance or glucagon tests. TSH, T4, PRL, LH, FSH, testosterone or oestradiol and plasma and urine osmolality were also measured. RESULTS: Post-operatively, 42% of patients achieved a mean GH level of < 5 mU/l. The success of surgery was related to the preoperative GH level; 65% of the patients with preoperative GH levels < 20 mU/l but only 18% of the patients with GH levels > 100 mU/l achieved post-operative GH values < 5 mU/l. In addition, tumour size influenced the outcome of surgery with 61% of patients with a microadenoma but only 23% of patients with a macroadenoma achieving post-operative GH levels of < 5 mU/l. Of the 42 patients considered in remission post-operatively (mean GH < 5 mU/l), 32 were available for long-term follow-up and were not offered any further treatment: only one of these has shown evidence of mild biochemical recurrence after a mean follow-up of 3.8 years (range 0.5-8). There were no peri-operative deaths. Two patients required surgical repair for CSF leaks and there were eight documented cases of meningitis. Permanent diabetes insipidus was noted in eight patients post-operatively. New anterior pituitary deficiency occurred in 21% of patients following surgery; 73% had unaltered pituitary function and in 6% recovery of partial hypopituitarism was noted. CONCLUSIONS: The stated outcome of surgery depends on the criteria adopted. Safe GH levels (mean levels < 5 mU/l) can be achieved in 42% of an unselected series of patients with acromegaly and if the tumour is a microadenoma this figure rises to 61%. Based on the current evidence it is safe not to offer further treatment to those patients in whom post-operative GH < 5 mU/l are achieved. 相似文献