全文获取类型
收费全文 | 6377篇 |
免费 | 494篇 |
国内免费 | 274篇 |
专业分类
电工技术 | 415篇 |
技术理论 | 1篇 |
综合类 | 258篇 |
化学工业 | 681篇 |
金属工艺 | 325篇 |
机械仪表 | 226篇 |
建筑科学 | 191篇 |
矿业工程 | 110篇 |
能源动力 | 179篇 |
轻工业 | 252篇 |
水利工程 | 77篇 |
石油天然气 | 108篇 |
武器工业 | 52篇 |
无线电 | 789篇 |
一般工业技术 | 543篇 |
冶金工业 | 2146篇 |
原子能技术 | 43篇 |
自动化技术 | 749篇 |
出版年
2024年 | 34篇 |
2023年 | 97篇 |
2022年 | 211篇 |
2021年 | 283篇 |
2020年 | 173篇 |
2019年 | 135篇 |
2018年 | 149篇 |
2017年 | 159篇 |
2016年 | 142篇 |
2015年 | 181篇 |
2014年 | 221篇 |
2013年 | 324篇 |
2012年 | 334篇 |
2011年 | 306篇 |
2010年 | 225篇 |
2009年 | 271篇 |
2008年 | 281篇 |
2007年 | 249篇 |
2006年 | 188篇 |
2005年 | 160篇 |
2004年 | 129篇 |
2003年 | 118篇 |
2002年 | 140篇 |
2001年 | 105篇 |
2000年 | 74篇 |
1999年 | 111篇 |
1998年 | 701篇 |
1997年 | 439篇 |
1996年 | 265篇 |
1995年 | 147篇 |
1994年 | 119篇 |
1993年 | 124篇 |
1992年 | 37篇 |
1991年 | 53篇 |
1990年 | 31篇 |
1989年 | 36篇 |
1988年 | 42篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1978年 | 5篇 |
1977年 | 44篇 |
1976年 | 102篇 |
1975年 | 10篇 |
1973年 | 6篇 |
排序方式: 共有7145条查询结果,搜索用时 15 毫秒
31.
Since the late 1980s, the eight-component model of the comprehensive school health program (CSHP), has been adopted widely in the United States and internationally. While it is acknowledged that the eight program elements should be delivered in a coordinated, interactive manner, numerous issues regarding how this integration best can be achieved, including who at the school level should have this responsibility and how the eight components relate conceptually and logistically, have not been addressed adequately. In essence, a CSHP transforms several solo performers into an orchestra. This article proposes the school health coordinator as an essential element in the eight-component model of the CSHP--the maestro, without whom there can be no symphony. The coordinator's principal responsibilities include administration, integration of personnel and programs, evaluation, and direct intervention. Three program elements--staff wellness, healthy environment, and community/family involvement--are subsumed within the coordinator's role, effectively reducing the number of program elements from eight to five. Potential benefits in addition to issues regarding feasibility of the SHC, are discussed and studies examining the effectiveness of the SHC model are recommended. 相似文献
32.
KR Kaderlik GJ Mulder RJ Turesky NP Lang CH Teitel MP Chiarelli FF Kadlubar 《Canadian Metallurgical Quarterly》1994,15(8):1695-1701
The food-borne carcinogenic and mutagenic heterocyclic aromatic amines undergo bioactivation to the corresponding N-hydroxy (OH)-arylamines and the subsequent N-glucuronidation of these metabolites is regarded as an important detoxification reaction. In this study, the rates of glucuronidation for the N-OH derivatives of 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP), 2-amino-6-methyl-dipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) by liver microsomal glucuronosyltransferase were compared to that of the proximate human urinary bladder carcinogen, N-OH-aminobiphenyl (N-OH-ABP) and the proximate rat colon carcinogen N-OH-3,2'-dimethyl-4-amino-biphenyl (N-OH-DMABP). Human liver microsomes catalyzed the uridine 5'-diphosphoglucuronic acid (UDPGA)-dependent glucuroidation of N-OH-IQ, N-OH-PhIP, N-OH-Glu-P-1 and N-OH-MeIQx at rates of 59%, 42%, 35% and 27%, respectively, of that measured for N-OH-ABP (11.5 nmol/min/mg). Rat liver microsomes also catalyzed the UDPGA-dependent glucuronidation of N-OH-PhIP, N-OH-Glu-P-1 and N-OH-IQ at rates of 30%, 20% and 10%, respectively of that measured for N-OH-DMABP (11.2 nmol/min/mg); activity towards N-OH-MeIQx was not detected. Two glucuronide(s) of N-OH-PhIP, designated I and II, were separated by HPLC. Conjugate II was found to be chromatographically and spectrally identical with a previously reported major biliary metabolite of PhIP in the rat, while conjugate I was identical with a major urinary metabolite of PhIP in the dog. Hepatic microsomes from rat, dog and human were found to catalyze the formation of both conjugates. The rat preferentially formed conjugate II (I to II ratio of 1:15), while the dog and human formed higher relative amounts of conjugate I (I to II ratio of 2.5:1.0 and 1.3:1.0 respectively). Fast atom bombardment mass spectrometry of conjugates I and II gave the corresponding molecular ions and showed nearly identical primary spectra. However, collision-induced spectra were distinct and were consistent with the identity of conjugates I and II as structural isomers. Moreover, the UV spectrum of conjugate I exhibited a lambda max at 317 nm and was essentially identical to that of N-OH-PhIP, while conjugate II was markedly different with a lambda max of 331 nm. Both conjugates were stable in 0.1 N HCl and were resistant to hydrolysis by rat, dog and human liver microsomal beta-glucuronidases.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
33.
There is agreement on the clinical diagnostic criteria for acute inflammatory demyelinating polyneuropathy (AIDP/GBS) however, there is lack of consensus for detection of demyelination. In order to critically evaluate the prevailing criteria, sixty-six patients who fulfilled NINCDS criteria and had typical features of GBS were studied for electrophysiological abnormalities of peripheral nerves by using standard methods (median, common peroneal, sural and ulnar) between 1 to 12 weeks after the onset of symptoms. The commonest abnormality on motor nerve conduction study was prolonged distal latency (75%-83%) followed by reduction in CMAP amplitude (63%-82%), decreased velocity (48%-62%), conduction block (17%-39%) and f-wave abnormalities (37.8%-59%). Sensory conduction abnormalities were detected in over 20% of median, 25% of ulnar and 33% of sural nerves. All the patients had abnormality of at least two motor conduction parameters in one nerve when values beyond 2 SD of the mean were considered abnormal and over 70% of patients had three abnormalities in two nerves or two abnormalities in three nerves. Comparison with the prevailing criteria for demyelination revealed that the number of patients fulfilling them varied widely: Albers et al. (1985): 74.2%, Albers et al. (1989): 40.9% and Cornblath: 30.3%. We believe that the current criteria for detection of demyelination in acute neuropathy are too strict, underestimate the underlying pathology in GBS and need reassessment. 相似文献
34.
The tail-flick (TF) technique was used to assess the antinociceptive properties of nifedipine (NIF) given intraperitoneally (i.p.). First, the most suitable intensity of the noxious stimulus (temperature of the bulb) has been ascertained and used in the main study. Male Sprague-Dawley rats received NIF, dissolved in dimethyl sulfoxide (DMSO) at the doses of 0.0, 0.5, 2, 5, 10 and 15 mg/kg, or control with no injection. For the main study, the noxious stimulus was limited to 15 sec (cut-off time) and TF latencies were recorded up to 120 min. The antinociceptive response was expressed as the area under the curve for each rat and analyzed by one-way ANOVA. The antinociceptive response to the lower doses of NIF (0.5 and 2 mg/kg) did not differ from control (no injection) and DMSO alone. Significance was found at 5, 10 and 15 mg NIF with no difference among the doses. However, there was an increasing tendency of the mean values from 0.5 to 15 mg NIF resulting in a positive correlation. The correlation coefficient was 0.32483 (p = 0.015) and regression equation Y = (19.37) x dose + 1320. Our data suggest that spinal mechanisms are involved in NIF-induced antinociception. 相似文献
35.
RH Rau YL Chan HI Chuang CR Cheng KL Wong KH Wu TT Wei 《Canadian Metallurgical Quarterly》1997,35(2):113-118
While current psychiatric taxonomies recognise a classification of amphetamine dependence, derived from the notion of an alcohol dependence syndrome, little research has validated that such a condition exists for this drug. Current amphetamine users (N = 331), were interviewed using the World Health Organization operationalisation of DSM-III-R substance dependence criteria, and a measure of the psychological components of dependence. Structural analyses indicated that a unidimensional dependence syndrome as assessed by DSM-III-R and DSM-IV criteria exists for amphetamine, and that physiological, psychological and behavioural indicators were all important in accounting for the variance in responses. It was demonstrated that the concept of a dependence syndrome is applicable to amphetamine, and that the inclusion of the amphetamine dependence syndrome in DSM-III-R and DSM-IV is valid. 相似文献
36.
CH Weaver LS Schwartzberg R Birch FA Greco S Rhinehart J Hainsworth T Beeker H Price L Geier J Foster J West B Hazelton CD Buckner 《Canadian Metallurgical Quarterly》1997,37(9):896-903
BACKGROUND: There is great interpatient variability in the number of peripheral blood stem cells collected, as measured by CD34+ cell content, after the administration of chemotherapy and a growth factor. The ability to predict patients who fail to yield adequate quantities of CD34+ cells would be of value. However, very few reports include large numbers of patients treated in an identical fashion. STUDY DESIGN AND METHODS: Between 1991 and 1995, 497 consecutive patients with a variety of malignant diseases received cyclophosphamide (4 g/m2), etoposide (600 mg/m2), and granulocyte-colony-stimulating factor (6 micrograms/kg/day) for mobilization and collection of a target dose > or = 2.5 x 10(8) CD34+ cells per kg. Multivariate analyses were performed to determine the factors associated with failure to achieve this target harvest. RESULTS: A median of 14.71 x 10(6) CD34+ cells per kg (range, 0.08-137.55) was harvested with a median of 2 (range, 1-11) apheresis procedures. Ninety-one percent of patients yielded > or = 2.5 x 10(5) CD34+ cells per kg. Patients with Stage II-III breast cancer, who had pretreatment platelet counts > or = 150 x 10(9) per L and patients who underwent < or = 1 prior chemotherapy regimen had improved CD34+ cell yields. However, most patients with adverse risk factors yielded > or = 2.5 x 10(6) CD34+ cells per kg. CONCLUSION: A regimen of cyclophosphamide, etoposide, and granulocyte-colony-stimulating factor led to the successful collection of adequate numbers of CD34+ cells in most patients without excessive toxicity. These observations confirm previous reports that intense prior therapy adversely affects the quantity of CD34+ cells harvested. Pretreatment and posttreatment variables did not predict with any certainty the small fraction of patients who fail to yield > or = 2.5 x 10(6) CD34+ cells per kg via multiple apheresis procedures. 相似文献
37.
38.
A wireless personal communications system, based on a TDMA architecture, using asynchronous ports (radio base stations) and the TDD (time division duplexing) method is evaluated using computer simulations. It is shown that, without port synchronisation TDD methods cannot achieve the uplink quality obtainable by the FDD (frequency division duplexing) method.<> 相似文献
39.
Taking into consideration a study published 10 years ago on sexual disturbances of students at the University of S?o Paulo, the importance of the subject is discussed, along with the creation in 1993 of the Sexuality Project at the university hospital of the University of S?o Paulo School of Medicine. In its first year, this multidisciplinary project attended 140 patients with sexual dysfunctions (associated or not to other clinical manifestations); the majority were younger than 60 years-old, and 80 percent were male. 相似文献
40.
HM Chaung CH Hong CP Chiang SK Lin YS Kuo WH Lan CC Hsieh 《Canadian Metallurgical Quarterly》1996,95(7):545-550
This review reports the different genetic factors that have been identified either as risk factor for Alzheimer's disease (AD) or directly causing the disease. First are reviewed epidemiological data and biological mechanisms about the apoplipoprotein E gene allele epsilon 4 that is a major risk factor for Alzheimer's disease. The second part describes the mutations responsible for early-onset autosomal dominant AD found in three different genes. The gene located on chromosome 21 encodes the amyloid precusor protein (APP). The presenilin 1 and presenilin 2 genes, located on chromosome 14 and 1 respectively, encode not yet known membrane proteins. 相似文献