全文获取类型
收费全文 | 2215篇 |
免费 | 14篇 |
专业分类
电工技术 | 9篇 |
综合类 | 1篇 |
化学工业 | 52篇 |
金属工艺 | 9篇 |
机械仪表 | 4篇 |
建筑科学 | 12篇 |
能源动力 | 15篇 |
轻工业 | 87篇 |
水利工程 | 3篇 |
石油天然气 | 1篇 |
无线电 | 92篇 |
一般工业技术 | 87篇 |
冶金工业 | 1786篇 |
原子能技术 | 13篇 |
自动化技术 | 58篇 |
出版年
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 22篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 25篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 10篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 19篇 |
2000年 | 8篇 |
1999年 | 55篇 |
1998年 | 521篇 |
1997年 | 305篇 |
1996年 | 189篇 |
1995年 | 117篇 |
1994年 | 108篇 |
1993年 | 110篇 |
1992年 | 17篇 |
1991年 | 37篇 |
1990年 | 27篇 |
1989年 | 29篇 |
1988年 | 23篇 |
1987年 | 34篇 |
1986年 | 27篇 |
1985年 | 33篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 13篇 |
1981年 | 17篇 |
1980年 | 22篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 50篇 |
1976年 | 119篇 |
1975年 | 11篇 |
1974年 | 5篇 |
1973年 | 5篇 |
排序方式: 共有2229条查询结果,搜索用时 15 毫秒
991.
992.
IM Sawhney PK Verma RK Dhiman JS Chopra A Sharma YK Chawla JB Dilawari 《Canadian Metallurgical Quarterly》1997,12(7):554-559
Evoked responses have not been studied in patients with acute severe hepatitis (ASH) with or without hepatic encephalopathy. This prospective study was undertaken to find out diagnostic as well as prognostic value of visual evoked responses (VER), and brain stem auditory evoked responses (BAER) in patients with ASH with or without encephalopathy. Visual evoked responses and BAER were studied in 20 patients (14 males and six females) with ASH. The patients were diagnosed as having severe hepatitis if acute hepatitis was associated with raised serum bilirubin and serum transaminases, and if they had a prothrombin time index of < 50%. After a detailed neuropsychiatric examination of each patient, the study sample was divided into two groups of 10 patients: ASH without encephalopathy (ASH-WOE), and ASH with encephalopathy (fulminant hepatic failure, FHF). The median P100 latencies of FHF patients were significantly increased compared with controls and patients in the ASH-WOE group. Abnormal P100 latencies, exceeding 95th percentile values of the controls, were present in one patient in the ASH-WOE group and six patients in the FHF group. The median interpeak latencies I-III, III-V and I-V were significantly prolonged in the FHF group. Interpeak latencies III-V were also increased significantly in patients in the ASH-WOE group. While abnormal BAER were seen frequently in both groups, VER abnormalities were largely confined to patients in the FHF group. In the FHF group, six out of 10 patients survived and exhibited clinical improvement in the status of hepatic encephalopathy. Evoked responses were repeated after 2-3 weeks of recovery in these patients and VER abnormalities showed a tendency to normalize, thereby suggesting a prognostic implication. The incidence of abnormal VER in hepatic encephalopathy complicating ASH far exceeded that of abnormal BAER. Markedly prolonged P100 latencies in FHF patients indicate poor prognosis. 相似文献
993.
In this report, 5 amino acid residues (aa) in the third cytoplasmic loop of the alpha 2D-adrenergic receptor are identified which (individually or together) alter its ligand-binding characteristics. An important structural discrepancy exists in the third cytoplasmic loop of the alpha 2D-ARs encoded by the rat cDNA and the rat gene--five aa are different. The newly identified bovine receptor as well as the mouse receptor contained the 5 aa identical to that encoded by the rat cDNA. Site-directed mutation of these residues to those of the rat gene encoded receptor resulted in alteration of binding characteristics: significant changes in the ability of the mutant receptor to bind to a number of agonists and antagonists were observed--ranging from a decrease by half in the case of oxymetazoline, to near total loss of binding in the case of prazosin. Thus, the mutant receptor was no longer pure alpha 2D-AR. This indicated a hitherto unrealized role of the third cytoplasmic loop in defining the ligand-binding characteristics of the receptor, and also suggested that the rat gene sequence was most probably in error. 相似文献
994.
The suspect role of the receptor-mediated cyclic GMP signaling pathway was dispelled by the discovery of a membrane guanylate cyclase that was also an atrial natriuretic factor receptor. It is now established that the membrane guanylate cyclase transduction system is linked to the signaling of natriuretic factors, guanylin/enterotoxin, and emerging evidence suggests that a new neural tissue-specific subfamily of membrane guanylate cyclases exists whose mechanism of signal transduction is different from those of the other membrane cyclases. This review will briefly discuss the fascinating, albeit turbulent, history of this signal transduction field, which will be followed by its current status and finally the direction it is heading. 相似文献
995.
The role of class I major histocompatibility complex (MHC) antigen levels on the ability of five murine tumour cell lines (YAC, P815, EL4, SP20 and L929) to competitively inhibit their own lysis, as well as the lysis of other targets by lymphokine-activated killer (LAK) effector cells was examined. Basal LAK susceptibilities of the cell lines were in the order P815 > YAC > SP20 > EL4 > L929, whereas the basal class I MHC antigen levels were in the order P815 > SP20 > L929 > YAC > EL4. Treatment with interferon-gamma (IFN-gamma) induced augmentation of class I MHC antigen levels on all cell lines. A concomitant decline in LAK susceptibility was seen for P815, YAC, SP20 and L929 cells, but not for EL4 target cells. On the basis of competition results, tumour cells appear to fall into two groups (group 1: P815, YAC and SP20; group 2: EL4 and L929). Members of each group could in general competitively inhibit the lysis of cell lines of their own group only. Treatment with IFN-gamma suppressed the ability of all tumour cell lines, except EL4, to cause competitive inhibition. These results support the proposition that class I MHC antigens may interfere with the recognition of target cells by effector LAK cells. 相似文献
996.
Amphotericin B (AmB)-resistant Leishmania donovani promastigotes were selected by increasing drug pressure, and their biological features were compared with those of the wild-type parent strain. The 50% inhibitory concentration for resistant cells was 20 times higher than that for the wild-type. Resistance was stable after more than 40 passages in drug-free medium, and resistant promastigotes were infective to macrophages in vitro but lost their virulence in vivo. They had 2.5 times longer generation time, decreased AmB uptake, and increased AmB efflux in comparison to the wild type. Fluorescence measurement with a specific plasma membrane probe, 1-[4-(trimethylammonio)-1,6-diphenylhexa]-1,3,5-triene, showed increased membrane fluidity in drug-resistant promastigotes. Analysis of lipid composition showed that in resistant cells saturated fatty acids were prevalent, with stearic acid as the major fatty acid, and the major sterol was an ergosterol precursor, the cholesta-5, 7, 24-trien-3beta-ol and not ergosterol as in the AmB-sensitive strain. 相似文献
997.
KC McCourt L Salmela RK Mirakhur M Carroll MT M?kinen M Kansanaho C Kerr GJ Roest KT Olkkola 《Canadian Metallurgical Quarterly》1998,53(9):867-871
Past investigations of in vivo arterial behavior have concentrated on determining material properties based upon the maximum and minimum pressure and diameter measured over a pulse cycle. A new in vivo technique, based upon continuous measurement of pressure and flow, has been developed to study arterial compliance throughout the pulse cycle. Compliance in the abdominal aorta of rats showed different behavior during the rising and falling portion of the pressure pulse. Previous investigations of canine arteries which used different methods are consistent with these findings. This study demonstrates the utility of a new measurement technique and shows some trends in compliance within the pulse cycle which have neither been revealed by static tests nor by dynamic tests which focused on pulse averaged values. 相似文献
998.
SL Wagner ER Peskind D Nochlin S Provow JS Farrow MR Pandian M Cleveland RK Ito MR Farlow 《Canadian Metallurgical Quarterly》1994,36(2):215-220
Cytogenetic analysis of four specimens (biopsy, definitive surgical, and two separately occurring lung metastases) of a dedifferentiated chondrosarcoma with a rhabdomyosarcomatous component revealed clonal karyotypic abnormalities in each. Anomalies seen in all specimens included a structurally aberrant chromosome 17 and extra copies of chromosomes 5, 7, 12, and 20. The derivation of the chromosomally abnormal cells was determined by a combined immunocytochemical/cytogenetic approach that allowed simultaneous assessment of cytogenetic aberrations and immunophenotypic features of individual cells. S-100 protein and desmin antibodies were used to evaluate the chondrosarcomatous and rhabdomyosarcomatous components, respectively. A chromosome 7-specific centromeric probe was used for determination of aneuploidy. In both specimens obtained from the primary lesion, S-100 protein and desmin-positive and -negative aneuploid cells were observed. These findings: 1) suggest that both the chondrocytic and rhabdomyoblastic cells arose from the same abnormal clone, 2) support the theory of a common primitive mesenchymal cell progenitor with the ability to differentiate or express features of more than one line of mesenchymal differentiation, and 3) indicate that the term dedifferentiated may be an inaccurate designation for this neoplasm. 相似文献
999.
1000.
RE Farrell 《Canadian Metallurgical Quarterly》1997,26(1-2):3-7
The polymerase chain reaction has become a mainstream tool for the molecular biologist. The sensitivity, efficiency, and speed of this method is unparalleled for the amplification and detection of exquisitely minute quantities of nucleic acids. Through repetitive cycles of heat denaturation of samples, followed by the base pairing of primers designed to identify one DNA sequence among the cellular heterogeneity, and finally synthesis of new DNA strands identical to the target, single molecules and individual genes can be detected and subsequently characterized. This method has revolutionized the study of gene organization, structure, and expression, not to mention offering newer, faster, and more economical means for the clinical detection infectious disease. That PCR has been fruitful is undisputed; however, the method is not without shortcomings. Among the major limitations of this method are the absolute requirement for well-designed primers, the super sensitivity of this method to biological contaminants from any of a variety of sources, and subtle, though very important, inter- and intra-laboratory variations in technique. 相似文献