全文获取类型
收费全文 | 1941篇 |
免费 | 0篇 |
专业分类
化学工业 | 10篇 |
机械仪表 | 1篇 |
轻工业 | 5篇 |
无线电 | 1篇 |
一般工业技术 | 1篇 |
冶金工业 | 1923篇 |
出版年
2022年 | 1篇 |
2013年 | 1篇 |
2011年 | 1篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2004年 | 1篇 |
2003年 | 2篇 |
1999年 | 65篇 |
1998年 | 580篇 |
1997年 | 309篇 |
1996年 | 186篇 |
1995年 | 102篇 |
1994年 | 117篇 |
1993年 | 113篇 |
1992年 | 6篇 |
1991年 | 19篇 |
1990年 | 21篇 |
1989年 | 28篇 |
1988年 | 28篇 |
1987年 | 22篇 |
1986年 | 23篇 |
1985年 | 22篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 66篇 |
1976年 | 160篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1941条查询结果,搜索用时 599 毫秒
41.
G Shi V Faúndez J Roos EC Dell''Angelica RB Kelly 《Canadian Metallurgical Quarterly》1998,143(4):947-955
Hereditary nonpolyposis colorectal cancer (HNPCC) is a syndrome involving a predisposition to cancers of the colon, endometrium and several other extra-colonic sites, accounting for approximately 1-5% of all colorectal cancer cases. It is not easily recognized because of a lack of distinctive clinical markers, making diagnosis and management of this disease problematic. To provide a basis for uniformity in diagnosis of HNPCC, the Amsterdam criteria were proposed and are currently in use. More recently, the discovery of four human mismatch repair genes (hMSH2, hMLH1, hPMS1 and hPMS2) has provided novel insight into the genetic basis of this disease, and raised the possibility of genetic diagnosis for management of HNPCC patients and their family members. This report summarizes the clinicopathologic aspects of HNPCC, reviews the recent genetic findings and surveillance strategies, and suggests a novel designation of certain patients as suspected HNPCC. 相似文献
42.
JB Thomas MJ Fall JB Cooper RB Rothman SW Mascarella H Xu JS Partilla CM Dersch KB McCullough BE Cantrell DM Zimmerman FI Carroll 《Canadian Metallurgical Quarterly》1998,41(26):5188-5197
A three-component library of compounds was prepared in parallel using multiple simultaneous solution-phase synthetic methodology. The compounds were biased toward opioid receptor antagonist activity by incorporating (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (a potent, nonselective opioid pure antagonist) as one of the monomers. The other two monomers, which included N-substituted or unsubstituted Boc-protected amino acids and a range of substituted aryl carboxylic acids, were selected to add chemical diversity. Screening of these compounds in competitive binding experiments with the kappa opioid receptor selective ligand [3H]U69,593 led to the discovery of a novel kappa opioid receptor selective ligand, N-?(2'S)-[3-(4-hydroxyphenyl)propanamido]-3'-methylbutyl?-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (8, RTI-5989-29). Additional structure-activity relationship studies suggested that 8 possesses lipophilic and hydrogen-bonding sites that are important to its opioid receptor potency and selectivity. These sites appear to exist predominantly within the kappa receptor since the selectivity arises from a 530-fold loss of affinity of 8 for the mu receptor and an 18-fold increase in affinity for the kappa receptor relative to the mu-selective ligand, (+)-N-[trans-4-phenyl-2-butenyl]-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (5a). The degree of selectivity observed in the radioligand binding experiments was not observed in the functional assay. According to its ability to inhibit agonist stimulated binding of [35S]GTPgammaS at all three opioid receptors, compound 8 behaves as a mu/kappa opioid receptor pure antagonist with negligible affinity for the delta receptor. 相似文献
43.
44.
CJ Frary RB Devereux R Kramer-Fox RB Roberts HS Ruchlin 《Canadian Metallurgical Quarterly》1994,73(4):263-267
In 1990-1991, a national survey was conducted to estimate the prevalence of Salmonella species among Canadian commercial turkey flocks. Two hundred and seventy flocks were randomly selected across Canada. The proportion sampled from each province was selected according to each province's share of the national turkey market. Samples, consisting of 12 pooled litter and four pooled dust samples, were used to determine the Salmonella status of the environment of each flock. Additionally, a one kilogram sample of feed was taken from each flock premise. Salmonella was recovered from environmental samples in 234/270 (86.7%) of flocks and from feed samples in 26/266 (9.8%) of flocks. Forty-eight different Salmonella serovars were isolated from flock environmental samples. The most prevalent serovars were S. anatum, S. hadar, S. agona, S. heidelberg and S. saintpaul which were isolated from 53/270 (19.6%), 49/270 (18.1%), 49/270 (18.1%), 42/270 (15.6%) and 34/270 (12.6%) flocks, respectively. 相似文献
45.
46.
The present study characterised seven species of the Chabertiidae (Nematoda: Strongyloidea) belonging to either the subfamily Oesophagostominae (Oesophagostomum radiatum, Oesophagostomum venulosum, Oesophagostomum dentatum, Oesophagostomum quadrispinulatum, Oesophagostomum columbianum, Oesophagostomum bifurcum) or to the subfamily Chabertiinae (Chabertia ovina) by their second internal transcribed spacer rDNA sequence, assessed the extent of intraspecific variation and interspecific differences in the sequence, and inferred the phylogenetic relationship of C. ovina with respect to members of the Oesophagostominae. In both the phenetic and cladistic analyses of the sequence data, Chabertia was nested within Oesophagostomum, suggesting either that the species examined represent members of the same genus, or alternatively, that Oesophagostomum may represent more than one genus. 相似文献
47.
The Drug Evaluation Classification Program: using ocular and other signs to detect drug intoxication
EM Kosnoski RL Yolton K Citek CE Hayes RB Evans 《Canadian Metallurgical Quarterly》1998,69(4):211-227
BACKGROUND: A systematic approach to determining drug intoxication has been developed for use by police officers. By considering specific physiological signs, trained officers can detect the effects of seven major drug types. METHODS: Officers follow a 12-step testing sequence and evaluate signs such as pupil sizes and responses, eye movements, heart rate, body temperature, mental timing, and balance. A matrix is then used to compare that subject's signs to those that would be produced by the seven types of drugs. If a pattern match is found, the officer concludes that the subject is under the influence of a drug and specifies the drug type. RESULTS: Several field and laboratory validation studies have been conducted using these procedures. In general, officers were 70% to 90% accurate in determining intoxication status and drug classification, but poly-drug use and drug rebound effects can sometimes cause problems in interpretation. CONCLUSION: Ocular and other physiological signs can be used to detect drug intoxication and classify the type of drug taken. Knowledge of the procedures used in the Drug Recognition Program can enable optometrists to serve as consultants to the police and as expert witnesses in cases involving the use of ocular signs that indicate illicit drug use. 相似文献
48.
D Matecka RB Rothman L Radesca BR de Costa CM Dersch JS Partilla A Pert JR Glowa FH Wojnicki KC Rice 《Canadian Metallurgical Quarterly》1996,39(24):4704-4716
The design, synthesis, and biological evaluation of compounds related to the dopamine (DA) uptake inhibitors: 1-[2-(diphenylmethoxy)ethyl]-4-(3-phenylpropyl)piperazine (1) and 1-[2-[bis-(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (2) (GBR 12395 and GBR 12909, respectively), directed toward the development and identification of new ligands interacting with high potency and selectivity at the dopamine transporter (DAT) is reported. The substitution of the piperazine ring in the GBR structure with other diamine moieties resulted in the retention of the high affinity of new ligands for the DAT. Some of the modified GBR analogs (e.g. 8, 10, (-)-49, or (-)-50) displayed substantially higher selectivity (4736- to 693-fold) for the dopamine (DA) versus the serotonin (5HT) reuptake site than the parent compounds. The bis(p-fluoro) substitution in the (diphenylmethoxy)ethyl fragment slightly increased the affinity of the ligands at the DA reuptake site but reduced their selectivity at this site (e.g. 9 and 8, 11 and 10, or 17 and 16, respectively). Congeners, such as the series of monosubstituted and symmetrically disubstituted piperazines and trans-2,5-dimethylpiperazines, which lack the (diphenylmethoxy)ethyl substituent lost the affinity for the DAT yet exhibited very high potency for binding to the sigma receptors (e.g.28). The chiral pyrrolidine derivatives of 1, (-)-49, and (+)-49, exhibited an enantioselectivity ratio of 181 and 146 for the inhibition of DA reuptake and binding to the DAT, respectively. 相似文献
49.
RT Malison LH Price R Berman CH van Dyck GH Pelton L Carpenter G Sanacora MJ Owens CB Nemeroff N Rajeevan RM Baldwin JP Seibyl RB Innis DS Charney 《Canadian Metallurgical Quarterly》1998,44(11):1090-1098
BACKGROUND: Prior research has suggested reductions in the density of serotonin transporter (SERT) binding sites in blood platelets and post-mortem brain tissue of depressed patients. We sought to determine whether patients with unipolar major depression have diminished SERT availability as assessed by both brainstem [123I] beta-CIT SPECT and platelet [3H]paroxetine binding. METHODS: Drug-free depressed and healthy subjects were injected with 211 +/- 22 MBq [123I] beta-CIT and imaged 24 +/- 2 h later under equilibrium conditions. A ratio of specific to nonspecific brain uptake (V3" = (brainstem-occipital)/occipital), a measure proportional to the binding potential (Bmax/Kd), was used for all comparisons. RESULTS: Results showed a statistically significant reduction in brainstem V3" values in depressed as compared to healthy subjects (3.1 +/- .9 vs. 3.8 +/- .8, p = .02). Platelet [3H]paroxetine binding was not altered (Bmax = 2389 +/- 484 vs. 2415 +/- 538 fmol/mg protein, p = .91) and was not significantly correlated with brainstem [123I] beta-CIT binding (r = -0.14, p = .48). CONCLUSIONS: These data are the first to suggest reductions in the density of brain SERT binding sites in living depressed patients. These findings provide further support for a preeminent role for alterations in serotonergic neurons in the pathophysiology of depression. 相似文献
50.
Rigid body rotation of five domains and movements within their interfacial joints provide a rational context for understanding why HIV protease mutations that arise in drug resistant strains are often spatially removed from the drug or substrate binding sites. Domain motions associated with substrate binding in the retroviral HIV-1 and SIV proteases are identified and characterized. These motions are in addition to closure of the flaps and result from rotations of approximately 6-7 degrees at primarily hydrophobic interfaces. A crystal structure of unliganded SIV protease (incorporating the point mutation Ser 4 His to stabilize the protease against autolysis) was determined to 2.0 A resolution in a new space group, P3221. The structure is in the most "open" conformation of any retroviral protease so far examined, with six residues of the flaps disordered. Comparison of this and unliganded HIV structures, with their respective liganded structures by difference distance matrixes identifies five domains of the protease dimer that move as rigid bodies against one another: one terminal domain encompassing the N- and C-terminal beta sheet of the dimer, two core domains containing the catalytic aspartic acids, and two flap domains. The two core domains rotate toward each other on substrate binding, reshaping the binding pocket. We therefore show that, for enzymes, mutations at interdomain interfaces that favor the unliganded form of the target active site will increase the off-rate of the inhibitor, allowing the substrate greater access for catalysis. This offers a mechanism of resistance to competitive inhibitors, especially when the forward enzymatic reaction rate exceeds the rate of substrate dissociation. 相似文献