首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1444篇
  免费   3篇
电工技术   1篇
化学工业   17篇
金属工艺   4篇
机械仪表   2篇
能源动力   13篇
轻工业   9篇
石油天然气   1篇
无线电   10篇
一般工业技术   15篇
冶金工业   1359篇
自动化技术   16篇
  2022年   1篇
  2021年   2篇
  2018年   2篇
  2016年   1篇
  2015年   1篇
  2014年   2篇
  2013年   9篇
  2012年   2篇
  2011年   7篇
  2010年   1篇
  2009年   4篇
  2008年   2篇
  2007年   5篇
  2006年   1篇
  2005年   3篇
  2004年   1篇
  2003年   4篇
  2001年   1篇
  2000年   2篇
  1999年   37篇
  1998年   448篇
  1997年   214篇
  1996年   169篇
  1995年   76篇
  1994年   64篇
  1993年   90篇
  1992年   12篇
  1991年   10篇
  1990年   16篇
  1989年   14篇
  1988年   19篇
  1987年   10篇
  1986年   11篇
  1985年   14篇
  1984年   4篇
  1983年   9篇
  1982年   9篇
  1981年   9篇
  1980年   10篇
  1979年   1篇
  1978年   3篇
  1977年   55篇
  1976年   84篇
  1975年   1篇
  1972年   2篇
  1970年   1篇
  1957年   1篇
  1955年   1篇
  1954年   1篇
  1949年   1篇
排序方式: 共有1447条查询结果,搜索用时 15 毫秒
41.
Ventriculo-peritoneal shunts (VPS) are the most frequent operative procedures used to treat hydrocephalic children. Abdominal complications of VPS are now a rare event; however, their frequency varies from 5% to 47% according to reports. Anything that causes an obstruction or impediment of the VP derivation system will lead to intracranial hypertension, which requires immediate surgery. From 1985 to 1995 at the Division of Pediatric Surgery of the Federico II University of Naples, ten laparoscopies were performed in ten children with VPS complications. Cerebrospinal fluid pseudocysts were found in four infants. There was one case of abdominal wall perforation by the tip of the catheter at the umbilical level, two bowel obstructions, and one catheter was lost in the abdominal cavity. Finally, two children had malfunctioning of the peritoneal limb of the catheter. The laparoscopic technique was curative in all ten cases, thus avoiding a conventional laparotomy and the consequent risk of adhesions, which could cause further complications.  相似文献   
42.
Analysis of the S-phase fractions (SPF) measured by in vitro thymidine labeling, morphological appearances, and estrogen receptor (ER) assays of primary invasive breast carcinomas demonstrated several interrelationships. Lobular, mucinous, tubular, and adenocystic carcinomas consistently had low SPF and were usually positive for ER. The same was true for the carcinomas of no special histologic type [the not otherwise specified (NOS) group of E. R. Fisher including "infiltrating ductal" and undifferentiated carcinomas] with minimal anaplasia. Medullary, atypical medullary, and morphologically unclassifiable carcinomas with marked nuclear anaplasia nearly always had high SPF and were usually negative for ER. High SPF was associated with advanced stages of carcinoma initially or with early recurrence following mastectomy.  相似文献   
43.
In a prospective study of twenty-six patients with ischemic ulcerations of the lower extremity, the predictive reliability with regard to spontaneous wound healing of diabetes, pedal pulses, ankle blood pressure (ABP) as measured by doppler ultrasound, and "leg ulcer scan" as performed by the intra-arterial injection of radioactive albumin was evaluated. The results suggest that only the leg ulcer scan is significantly reliable in predicting the likelihood of spontaneous healing. The following format for the evaluation of the ischemic leg ulcer is therefore suggested: (1) If pedal pulses are present, a three week trial of conservative therapy is indicated before further evaluation. (2) If the doppler ABP is 50 mm Hg or less, the ulcer will not heal spontaneously. (3) Leg ulcer scan is indicated: (a) in the absence of pedal pulses if ABP is less than 50 mm Hg; (b) in the presence of pedal pulses if there is no evidence of spontaneous healing after three weeks of conservative therapy.  相似文献   
44.
Experiments were performed on obligatory bipeds to study the effects of an arteriovenous fistula on a devascularized ischemic limb. Retrograde flow of arterial blood entering the venous system by way of an arteriovenous fistula was demonstrated. Venous valves appeared not to interfere with retrograde arterial flow. The data from these experiments indicate that a "Y" type arteriovenous fistula can lead to functional revascularization in the ischemic limb with arterial obstruction. The dual mechanism of retrograde arterial flow in venous channels and the stimulation of collateral flow adjacent to the fistula seemed to be critical factors. Since a peripheral arteriovenous fistula is a potent stimulus to arterial collateralization in the extremity, its application is worthy of consideration in certain selected patients with advanced and otherwise inoperable arterial occlusive disease.  相似文献   
45.
The B-cell lymphoma-2 (Bcl-2) family is a group of genes regulating intrinsic apoptosis, a process controlling events such as development, homeostasis and the innate and adaptive immune responses in metazoans. In higher organisms, Bcl-2 proteins coordinate intrinsic apoptosis through their regulation of the integrity of the mitochondrial outer membrane; this function appears to have originated in the basal metazoans. Bcl-2 genes predate the cnidarian-bilaterian split and have been identified in porifera, placozoans and cnidarians but not ctenophores and some nematodes. The Bcl-2 family is composed of two groups of proteins, one with an α-helical Bcl-2 fold that has been identified in porifera, placozoans, cnidarians, and almost all higher bilaterians. The second group of proteins, the BH3-only group, has little sequence conservation and less well-defined structures and is found in cnidarians and most bilaterians, but not porifera or placozoans. Here we examine the evolutionary relationships between Bcl-2 proteins. We show that the structures of the Bcl-2-fold proteins are highly conserved over evolutionary time. Some metazoans such as the urochordate Oikopleura dioica have lost all Bcl-2 family members. This gene loss indicates that Bcl-2 regulated apoptosis is not an absolute requirement in metazoans, a finding mirrored in recent gene deletion studies in mice. Sequence analysis suggests that at least some Bcl-2 proteins lack the ability to bind BH3-only antagonists and therefore potentially have other non-apoptotic functions. By examining the foundations of the Bcl-2 regulated apoptosis, functional relationships may be clarified that allow us to understand the role of specific Bcl-2 proteins in evolution and disease.  相似文献   
46.
An outbreak of gastroenteritis in a school district in the United States was determined to be staphylococcal food poisoning due to 2% chocolate milk containing staphylococcal enterotoxin A (SEA). Twelve one-half pint (approx 0.28 l) cartons of the 2% chocolate milk from this outbreak were analyzed for the quantity of SEA present in the milk. The amount of SEA in the cartons varied from 94 to 184 ng with the average being 144 ng (mean = 139 +/- 45). The attack rate for vomiting among those who consumed more than one carton was greater (38.3%) than among those who consumed only one carton (31.5%) with the highest attack rate among those who consumed three or more cartons (44.4%).  相似文献   
47.
48.
A 20000-gate GaAs array with 10 K of embedded RAM is presented. The array contains eight scannable fully registered 256×256 RAM macros which have a minimum cycle time of 3.5 ns. The RAM features a scan mode, which can be used to configure the registers into a serial shifter. There is also a RAM test mode which allows independent functional and speed testing of all eight RAMs, easing the task of RAM verification for a given user personalization. The RAM array was fabricated using an advanced high-performance GaAs semiconductor E /D MESFET process featuring self-aligned gates and requiring only 12 masks. Introductory discussion of the Vitesse GaAs process, basic GaAs MESFET characteristics, and GaAs circuit design are provided. The gate array portion contains 20736 user-configurable cells with 10-ps gate delays which are tailored for direct-coupled FET logic (DCFL). The I/O can be personalized for ECL, TTL, or GaAs levels. There are 392 pads on the 13.8-mm×7.7-mm die with a maximum of 256 used for signal I/O. The RAM array is packaged in a multilayer ceramic 344-pin leaded chip carrier (LDCC). Typical power dissipation at 80% utilization is 14 W  相似文献   
49.
Exposure of mammalian cells to ultraviolet (UV) light elicits a cellular response and can also lead to apoptotic cell death. In this report, we show that a 36-kDa myelin basic protein (MBP) kinase detected by an in-gel kinase assay can be dramatically activated during the early stages of UV irradiation-triggered apoptosis of A431 cells. Immunoblot analysis revealed that this 36-kDa MBP kinase could be recognized by an antibody against the C-terminal regions of a family of p21Cdc42/Rac-activated kinases (PAKs). By using this antibody and a PAK2-specific antibody against the N-terminal region of PAK2 as studying tools, we further demonstrated that UV irradiation caused cleavage of PAK2 to generate a 36-kDa C-terminal catalytic fragment and a 30-kDa N-terminal fragment in A431 cells. The appearance of the 36-kDa C-terminal catalytic fragment of PAK2 matched exactly with the activation of the 36-kDa MBP kinase in A431 cells upon UV irradiation. In addition, UV irradiation also led to activation of CPP32/caspase-3, but not ICH-1L/caspase-2 and ICE/caspase-1, in A431 cells and the kinetics of activation of CPP32/caspase-3 appeared to correlate well with that of DNA fragmentation and of cleavage/activation of PAK2, respectively. Moreover, blockage of activation of CPP32/caspase-3 by pretreating the cells with two specific tetrapeptidic inhibitors for caspases (Ac-DEVD-cho and Ac-YVAD-cmk) could significantly attenuate the extent of cleavage/activation of PAK2 induced by UV irradiation. Collectively, the results demonstrate that cleavage and activation of PAK2 can be induced during the early stages of UV irradiation-triggered apoptosis and indicate the involvement of CPP32/caspase-3 in this process.  相似文献   
50.
The particle size distribution and the metal speciation of the heavy metals were investigated on dredged sediment and on the fractions obtained by mechanical agitated (Denver) flotation. The transition metal ions (cadmium, copper, lead and zinc) were flotated specifically independent of the particle size. Particle size analysis, EDTA extraction and sequential extracts indicated that during flotation a redistribution of metals occurred due to the oxidation of metal sulphides. This oxidation process was more pronounced when the flotation was performed at higher pH values and resulted in a decrease in flotation specificity.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号