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   1978篇
  免费   3篇
  国内免费   3篇
电工技术   2篇
综合类   2篇
化学工业   11篇
金属工艺   2篇
机械仪表   1篇
建筑科学   3篇
矿业工程   1篇
轻工业   6篇
水利工程   1篇
石油天然气   1篇
武器工业   1篇
无线电   3篇
一般工业技术   5篇
冶金工业   1935篇
自动化技术   10篇
  2016年   2篇
  2014年   1篇
  2013年   7篇
  2011年   2篇
  2008年   2篇
  2007年   1篇
  2005年   1篇
  2004年   5篇
  2003年   10篇
  2002年   2篇
  2001年   1篇
  2000年   2篇
  1999年   60篇
  1998年   634篇
  1997年   374篇
  1996年   203篇
  1995年   111篇
  1994年   107篇
  1993年   132篇
  1992年   12篇
  1991年   28篇
  1990年   22篇
  1989年   26篇
  1988年   23篇
  1987年   24篇
  1986年   13篇
  1985年   19篇
  1983年   2篇
  1982年   5篇
  1981年   12篇
  1980年   12篇
  1978年   4篇
  1977年   45篇
  1976年   76篇
  1975年   1篇
  1964年   1篇
  1955年   2篇
排序方式: 共有1984条查询结果,搜索用时 15 毫秒
71.
CONTEXT: Disputes associated with achieving recognition for work done may affect both morale and subsequent resource allocation to medical researchers. OBJECTIVE: To assess authorship disputes brought to the Ombuds Office. SETTING: The Ombuds Office, Harvard Medical School, Dental School, School of Public Health, and affiliated hospitals. MAIN OUTCOME MEASURE: Change in number of queries related to authorship between 1991 to 1992 and 1996 to 1997. RESULTS: Disputes increased from 8 (2.3%) of 355 issues brought to the office in 1991 to 1992 to 59 (10.7%) of 551 issues in 1996 to 1997. They also increased from involving 0.06% of the total population of faculty, staff, and students affiliated with the schools in 1991 to 1992 to 0.33% of the total population in 1996 to 1997. Such problems appear to occur more often for women (53% of complaints in 1994-1995 through 1996-1997) and for non-US citizens (21 % of complaints in 1991-1992 through 1996-1997). CONCLUSIONS: Authorship disputes are increasingly frequent. Institutions should increase enforcement of published authorship standards and place more emphasis on managerial skills for laboratory and research department heads.  相似文献   
72.
By limiting galactosylation mechanisms, a cellular deficiency of the uridine sugar nucleotide, UDPgalactose, has been implicated as a cause of the long-term complications seen in patients with classic galactosemia despite dietary treatment. As a result, great interest has been generated in the accurate assessment of UDPgalactose, as well as UDPglucose, from which UDPgalactose may be derived by the function of a ubiquitous, active UDPgalactose-4-epimerase. Since several series of values for the concentration of these compounds in red blood cells (RBCs) of galactosemics have been flawed by the use of methods subsequently shown to be unsuitable, we have quantified erythrocyte UDPgalactose and UDPglucose levels by an accurate high-performance liquid chromatography (HPLC) assay in 116 normals, 76 galactosemics, and 39 patients with other metabolic disorders. These large groups have permitted the evaluation of age, diet, and genotype as influential factors in the steady-state RBC levels of the sugar nucleotides. The data show that age is an important determinant of RBC levels, with children younger than 10 years having higher values than individuals older than 10 years. Mean UDPgalactose levels in galactosemic children younger than 10 years and those older than 10 years were 30% and 18% lower, respectively, than levels in comparable normals. Although the mean differences were highly significant, there was considerable overlap of individual values. There was no difference in UDPglucose levels between galactosemics and normals.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
73.
AIMS: To determine the survival and disability rates at 7-8 years in infants of less than 28 weeks gestation born in New Zealand in 1986 and admitted to a neonatal unit. METHODS: In 1986, all infants with birthweight less than 1500 g and admitted to neonatal units were enrolled in a prospective audit of retinopathy of prematurity. Surviving infants, including the subset born at less than 28 weeks gestation, have been assessed at a home visit. Parents completed a comprehensive questionnaire and children underwent a visual assessment and were tested on the Wechsler Intelligence Scale for Children. RESULTS: Of 126 liveborn infants less than 28 weeks gestation, 80 (64%) survived to 7-8 years. Sixty eight children (97% survivors resident in New Zealand) were assessed: 72% had no, and 86% no or only mild disability, 77% had some visual problem, with close to one-third having myopia, strabismus or requiring spectacles and 32% received Ministry of Education funded special needs assistance. CONCLUSIONS: There have been few long-term follow-up studies of infants of less than 28 weeks gestation born in a defined geographical area. The outcome for New Zealand infants is comparable with that in other published data.  相似文献   
74.
75.
OBJECTIVE: This study determined the sources and frequency of diagnostic uncertainty for patients with chronic psychosis and active cocaine abuse or dependence and assessed the usefulness of prospective follow-up in clarifying diagnosis. METHODS: A total of 165 male patients with chronic psychoses and cocaine abuse or dependence on inpatient units of a Veterans Affairs medical center were evaluated using the Structured Clinical Interview for DSM-III-R (SCID-R), urine tests, hospital records, and interviews with collateral sources. An algorithm allowing key SCID-R items and diagnostic criteria to be designated as provisionally met or uncertain was applied, resulting in a provisional diagnosis and a list of alternate diagnoses. The assessment was repeated 18 months later in an attempt to resolve diagnostic uncertainty. RESULTS: In 30 cases (18 percent), initial assessment produced a definitive diagnosis, including 21 cases of schizophrenia, six of schizoaffective disorder, and three of psychostimulant-induced psychotic disorder. In the other 135 cases, a definitive diagnosis could not be reached because of one or more sources of diagnostic uncertainty, including insufficient periods of abstinence (78 percent), poor memory (24 percent), and inconsistent reporting (20 percent). Reassessment at 18 months led to definitive diagnoses in 12 additional cases. CONCLUSIONS: It was frequently difficult to distinguish schizophrenia from chronic substance-induced psychoses. Rather than concluding prematurely that psychotic symptoms are, or are not, substance induced, clinicians should initiate treatment of both psychosis and the substance use disorder in uncertain cases. The persistence or resolution of psychosis during abstinence and additional history from the stabilized patient or collateral sources may clarify the diagnosis.  相似文献   
76.
Salvia divinorum is a vision-inducing mint used by the Mazatec people of Oaxaca, Mexico. It is grown in California and other parts of the United States where it is employed as a legal hallucinogen. Traditional opinion has been that the plant has mild psychotropic activity, at best. However, when ingested in the correct manner, it is quite powerful. The fresh leaves are chewed as a quid and kept in the mouth. They may also be eaten raw or prepared as an aqueous infusion. When dried, they are smoked in the manner of marijuana. The neoclerodane diterpene, salvinorin A (also known as divinorin A), has been demonstrated in animals and humans to be its major active ingredient. Essentially inactive if taken orally, the compound is effective in doses of 200 to 500 mcg when smoked in a manner similar to cocaine free base. This makes salvinorin A the first documented diterpene hallucinogen and the most potent naturally occurring hallucinogen thus far isolated. This is somewhat remarkable, since the compound is not an alkaloid. This article reviews the use of S. divinorum and its chemistry. In addition, it discusses the effects of the plant and salvinorin A in animals and humans, as well as their potential to become drugs of abuse.  相似文献   
77.
BACKGROUND: Significant changes are restructurng the U.S. health care delivery system. National health reform is now extending itself into the public sector. Increased health and medical costs by federal and state governments are forcing a reevaluation of major entitlement programs, especially Medicaid. METHODS/RESULTS: Because Medicaid is the single largest item in many state budgets, states are now enrolling Medicaid patients into managed and coordinated care arrangements as a means to control costs and increase access to care. HMOs are not only competing for private patients but also actively seeking the Medicaid population. Nationally, almost one-fourth of all Medicaid patients are now enrolled in managed care plans. Various models and approaches have been developed by individual states. CONCLUSIONS: Because managed care enrollment in the Medicaid program has increased substantially in recent years, selected services including vision care are no longer rendered by any practitioner willing to accept Medicaid fees. Freedom of choice is now restricted to pre-selected and panel practitioners participating with the managed care program. The rules, regulations, billing procedures, fees, and program requisites will differ under managed care programs. Private optometric practitioners must consider entering economic and organizational relationships and linkages that make them attractive to managed care organizations.  相似文献   
78.
We isolated cDNA clones encoding five S-RNases (S1-, S3-, S5-, S6-, S7-RNases) from pistils of Pyrus pyrifolia (Japanese pear), a member of the Rosaceae. Their amino acid sequences were aligned with those of other rosaceous S-RNases sequenced so far. A total of 76 conserved amino acid residues were stretched throughout the sequence, but were absent from the 51-66 region which was designated the hypervariable (HV) region. The phylogenetic tree of rosaceous S-RNases showed that S-RNase polymorphism predated the divergence of Pyrus and Malus. Pairwise comparison of these S-RNases detected two highly homologous pairs, P. pyrifolia S1- and S4-RNases (90.0%) and P. pyrifolia S3- and S5-RNases (95.5%). The positions of amino acid substitutions between S1- and S4-RNases were spread over the entire region, but in the pair of S3- and S5-RNases, amino acid substitutions were found in the 21-90 region including the HV region. The substitutions in this restricted region appear to be sufficient to discriminate between S3 and S5 pollen and to trigger the self-incompatible reaction.  相似文献   
79.
The behavioral effects were studied of monoclonal antibodies (MA) against A3G7 protein, which is known to be associated with the processes of nervous cell differentiation. Elaboration, storage, and retention of acoustic startle (ASR) habituation and freezing behavior were tested in adult rats. The MA applied in a dose of 50 ng on cerebellar vermis selectively impaired only the ASR long-term habituation storage whereas its dose of 5 mcg impaired both long-term habituation storage and fear-conditioned freezing. Application of 10 mcg of MA disrupted the elaboration and storage of the ASR short- and long-term habituation as well as fear-conditioned freezing. The results are considered as experimental verification of systemogenesis theory and hypothesis about a common molecular basis of learning and development.  相似文献   
80.
In the Netherlands, childhood leukaemia is recorded by the Dutch Childhood Leukaemia Study Group (DCLSG, set up in 1972) and by nine regional cancer registries which together form the Netherlands Cancer Registry (NCR, set up in 1989). The data files from the incidence years 1989-1992 of the two registries were linked in order to evaluate accuracy and completeness and to calculate and equalise the incidence rates for childhood leukaemia in The Netherlands. Unlinked records or records with disagreements (birth date, sex, type of leukaemia and incidence date) were checked by the DCLSG and by the regional cancer registries. The DCLSG recorded 431 cases of childhood leukaemia, while the NCR recorded 434 cases. After record linkage and review of the cases, it was concluded the 445 records should have been recorded as childhood leukaemia. The NCR had recorded 425 of the 445 correct cases (95.5%), but had missed 20 cases (4.5%). The DCLSG had recorded 431 of the 445 correct cases (96.9%) and had missed 14 cases (3.1%). In addition, the NCR had recorded 9 cases incorrectly as childhood leukaemia. Part of the disagreement was caused by differences in coding rules (definition of non-Hodgkin's lymphoma (NHL) and the myelodysplastic syndrome versus leukaemia). It could be concluded that the quality and completeness of the two registries was very high. Regular comparison of the recorded data will help to reveal the inherently problematic disagreement between definitions and coding.  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