全文获取类型
收费全文 | 1887篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 7篇 |
化学工业 | 79篇 |
金属工艺 | 16篇 |
机械仪表 | 9篇 |
建筑科学 | 10篇 |
矿业工程 | 1篇 |
能源动力 | 12篇 |
轻工业 | 49篇 |
水利工程 | 8篇 |
石油天然气 | 1篇 |
无线电 | 87篇 |
一般工业技术 | 70篇 |
冶金工业 | 1492篇 |
原子能技术 | 5篇 |
自动化技术 | 56篇 |
出版年
2022年 | 9篇 |
2021年 | 10篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 7篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 27篇 |
2012年 | 11篇 |
2011年 | 25篇 |
2010年 | 10篇 |
2009年 | 17篇 |
2008年 | 13篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 21篇 |
2004年 | 17篇 |
2003年 | 17篇 |
2002年 | 18篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 54篇 |
1998年 | 400篇 |
1997年 | 230篇 |
1996年 | 163篇 |
1995年 | 91篇 |
1994年 | 82篇 |
1993年 | 89篇 |
1992年 | 19篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 32篇 |
1987年 | 41篇 |
1986年 | 31篇 |
1985年 | 20篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 11篇 |
1980年 | 30篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 36篇 |
1976年 | 111篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1970年 | 4篇 |
1964年 | 3篇 |
排序方式: 共有1902条查询结果,搜索用时 78 毫秒
61.
62.
63.
Stanley GB 《Neural computation》2002,14(12):2925-2946
The encoding properties of the visual pathway are under constant control from mechanisms of adaptation and systems-level plasticity. In all but the most artificial experimental conditions, these mechanisms serve to continuously modulate the spatial and temporal receptive field (RF) dynamics. Conventional reverse-correlation techniques designed to capture spatiotemporal RF properties assume invariant stimulus-response relationships over experimental trials and are thus limited in their applicability to more natural experimental conditions. Presented here is an approach to tracking time-varying encoding dynamics in the early visual pathway based on adaptive estimation of the spatiotemporal RF in the time domain. Simulations and experimental data from the lateral geniculate nucleus reveal that subtle features of encoding properties can be captured by the adaptive approach that would otherwise be undetected. Capturing the role of dynamically varying encoding mechanisms is vital to our understanding of vision on the natural setting, where there is absence of a true steady state. 相似文献
64.
Ronald J Duchovic Yuri L VolobuevGillian C Lynch Donald G TruhlarThomas C Allison Albert F WagnerBruce C Garrett Jose C Corchado 《Computer Physics Communications》2002,144(2):169-187
POTLIB 2001 is a computer program library of global chemical potential energy surface (PES) functions (91 functions in version 1.0) along with test data, a suite of utility programs, and a convenient user interface. The PES programs are written in ANSI standard FORTRAN77 and can be used to determine the Born-Oppenheimer potential energy of chemical systems as a function of the internal coordinates. The accompanying test data allow users to verify local implementations of this library. Finally, the utility programs permit use of this library in conjunction with a variety of chemical dynamics and chemical kinetics computer codes. Interface routines are provided for the POLYRATE and ABCRATE program packages of Truhlar and co-workers, the VENUS96 program package of Hase and co-workers, and the VARIFLEX program package of Klippenstein and co-workers; the routines in this library can also be used in conjunction with the DYNASOL program package of Zhang and co-workers. This article describes the library and the utility programs and outlines the systematic conventions used for interfaces in the computer programs contained in the library. Adherence to these conventions will allow future PESs to be compatible with this library. 相似文献
65.
Seventy-eight Holsteins were fed for 112 d to evaluate performance and health responses to diets varying in source and concentration of fiber. Three diets based on different carbohydrate feeding strategies were formulated. These diets contained low concentrations of forage and neutral detergent fiber (NDF) (12.6% forage NDF, 19.5% total NDF), adequate NDF and forage (20% forage NDF, 24.8% total NDF), or low forage with additional NDF from cereal byproducts (12.7% forage NDF, 33.4% total NDF). Responses to sodium bicarbonate supplementation (0 or 0.8% of diet DM) were evaluated for each carbohydrate strategy, and bicarbonate improved performance on all diets. Eight cows were used concurrently in a Latin square experiment to evaluate the linearity of milk fat concentration response to increasing concentrations of byproduct NDF in low-forage diets. Considering both trials, cereal byproduct NDF was only 27% as effective as NDF from alfalfa silage in eliciting a milk fat concentration response, which was less than predicted from previous experiments. This difference was not because of the short duration of previous experiments nor because of nonlinearity in the response to byproduct NDF. Low-forage diets fed for 112 d did not result in major health disorders for midlactation cows. However, several indicators suggested that cows fed low-forage, high-NDF diets might be less susceptible to ruminal acidosis than those fed diets containing low forage and low NDF, especially during times of dietary transition. Although the effective fiber value in various feeds is variable and difficult to quantify, the value of byproduct fiber needs to be considered when balancing the carbohydrate fraction of dairy rations. 相似文献
66.
Caveolae are small microdomains of the plasma membrane that are thought to play important roles in signal transduction processes. In this work, we have investigated the association of Rho proteins with caveolae-enriched membrane domains isolated from cultured endothelial cells. Fractionation of ECV304 cells by sucrose gradient density centrifugation in the absence of detergent resulted in the co-sedimentation of a significant proportion of RhoA and Cdc42 with known caveolae marker proteins, including caveolin, but not with other non-caveolae membrane proteins such as the angiotensin-converting enzyme. Immunoprecipitation experiments carried on crude endothelial cell lysates as well as with solubilized caveolae-enriched membrane domains showed the coimmunoprecipitation of caveolin with RhoA but not with Cdc42. Incubation of endothelial cell lysates with a glutathione-S-transferase (GST)-RhoA fusion protein resulted in the specific precipitation of caveolin, while addition of GST-caveolin-1 to the lysates promoted the precipitation of RhoA. Moreover, incubation of bacterially expressed RhoA with GST-caveolin-1 resulted in the precipitation of RhoA, indicating that RhoA directly interacts with caveolin-1. This interaction was found to be nucleotide-independent and was not affected by prior modification of RhoA with the C3 exoenzyme from C. botulinium or with the cytotoxic necrotinizing factor from E. coli. Taken together, these results suggest the association of RhoA with endothelial caveolae-enriched membrane domains, likely through physical interaction with caveolin-1. These findings may provide new insights into the functions played by Rho proteins and caveolae in signal transduction events. 相似文献
67.
KP Papadopoulos JH Garvin M Fetell LT Vahdat TJ Garrett DG Savage C Balmaceda J Bruce M Sisti S Isaacson R De LaPaz R Hawks E Bagiella KH Antman CS Hesdorffer 《Canadian Metallurgical Quarterly》1998,22(7):661-667
The prognosis in patients with primary brain tumors treated with surgery, radiotherapy and conventional chemotherapy remains poor. To improve outcome, combination high-dose chemotherapy (HDC) has been explored in children, but rarely in adults. This study was performed to determine the tolerability of three-drug combination high-dose thiotepa (T) and etoposide (E)-based regimens in pediatric and adult patients with high-risk or recurrent primary brain tumors. Thirty-one patients (13 children and 18 adults) with brain tumors were treated with high-dose chemotherapy: 19 with BCNU (B) and TE (BTE regimen), and 12 with carboplatin (C) and TE (CTE regimen). Patients received growth factors and hematopoietic support with marrow (n = 15), peripheral blood progenitor cells (PBPC) (n = 11) or both (n = 5). The 100 day toxic mortality rate was 3% (1/31). Grade III/IV toxicities included mucositis (58%), hepatitis (39%) and diarrhea (42%). Five patients had seizures and two had transient encephalopathy (23%). All patients had neutropenic fever and all pediatric patients required hyperalimentation. Median time to engraftment with absolute neutrophil count (ANC) >0.5 x 10(9)/l was 11 days (range 8-37 days). Time to ANC engraftment was significantly longer (P = 0.0001) in patients receiving marrow (median 14 days, range 10-37) than for PBPC (median 9.5 days, range 8-10). Platelet engraftment >50 x 10(9)/l was 24 days (range 14-53 days) in children. In adults, platelet engraftment >20 x 10(9)/l was 12 days (range 9-65 days). In 11 patients supported with PBPC, there was a significant inverse correlation between CD34+ dose and days to ANC (rho = -0.87, P = 0.009) and platelet engraftment (rho = -0.85, P = 0.005), with CD34+ dose predicting time to engraftment following HDC. Overall, 30% of evaluable patients (7/24) had a complete response (CR) (n = 3) or partial response (PR) (n = 4). Median time to tumor progression (TTP) was 7 months, with an overall median survival of 12 months. These TE-based BCNU or carboplatin three-drug combination HDC regimens are safe and tolerable with promising response rates in both children and older adults. 相似文献
68.
The anatomy of cranial nerves I and III through XII are presented. Each nerve is diagrammatically illustrated from its nuclear or its sensory origin and correlated with magnetic resonance and computed tomography images. The important identifying anatomical landmarks are demonstrated along the course of each nerve. Peripheral motor and sensory components are also discussed. 相似文献
69.
H Westergren A Holtz M Farooque WR Yu Y Olsson 《Canadian Metallurgical Quarterly》1998,15(11):943-954
This article addresses one basic issue regarding the use of systemic hypothermia in the acute management of spinal cord injury, namely, how to interpret temperature recordings in accessible organs such as the rectum or esophagus with reference to the spinal cord temperature. Thirty-six rats, divided into six groups, were randomized to laminectomy or to severe spinal cord compression trauma, and were further randomized to either a cooling/rewarming procedure or continuous normothermia (esophageal temperature 38 degrees C) for 90 min. The first procedure comprised normothermia during the surgical procedure, followed by lowering of the esophageal temperature from 38 degrees C to 30 degrees C (the hypothermic level), a 20-min steady-state period at 30 degrees C, rewarming to 38 degrees C, and finally a 20-min steady-state period at 38 degrees C. The esophageal, rectal, and epidural temperatures were recorded in all animals. The intramedullary temperature was also recorded invasively in four of the six groups. We conclude that the esophageal temperature is safe and easy to record and, in our setting, reflects the epidural temperature. The differences registrated may reflect a true deviation of the intramedullary temperature due to initial environmental exposure and secondary injury processes. Our results indicate that the esophageal temperature exceeds the intramedullary temperature during the initial recording and final steady state following rewarming, but not during the most crucial part of the experiment, the hypothermic period. The core temperature measured in the esophagus can therefore be used to evaluate the intramedullary temperature during alterations of the systemic temperature and during hypothermic periods. 相似文献
70.
OBJECTIVE: To review the literature investigating the effects of parental affective illness on children over the past decade. METHOD: A computerized search of articles published over the past 10 years was completed. Articles were reviewed and relevant studies are presented. RESULTS: Over the course of the past 10 years a number of longitudinal studies have confirmed that children of affectively ill parents are at a greater risk for psychiatric disorders than children from homes with non-ill parents. Life table estimates indicate that by the age of 20 a child with an affectively ill parent has a 40% chance of experiencing an episode of major depression. Children from homes with affectively ill parents are more likely to exhibit general difficulties in functioning, increased guilt, and interpersonal difficulties as well as problems with attachment. Marital difficulties, parenting problems, and chronicity and severity of parental affective illness have been associated with the increased rates of disorder observed in these children. CONCLUSION: The presence of depression in parents should alert clinicians to the fact that their children also may be depressed and therefore in need of services. J. Am. Acad. Child Adolesc. 相似文献