全文获取类型
收费全文 | 44733篇 |
免费 | 4048篇 |
国内免费 | 31篇 |
出版年
2022年 | 283篇 |
2021年 | 619篇 |
2020年 | 410篇 |
2019年 | 503篇 |
2018年 | 668篇 |
2017年 | 572篇 |
2016年 | 1073篇 |
2015年 | 1810篇 |
2014年 | 1947篇 |
2013年 | 2527篇 |
2012年 | 3075篇 |
2011年 | 3144篇 |
2010年 | 2008篇 |
2009年 | 1705篇 |
2008年 | 2604篇 |
2007年 | 2579篇 |
2006年 | 2335篇 |
2005年 | 2394篇 |
2004年 | 2352篇 |
2003年 | 2239篇 |
2002年 | 2189篇 |
2001年 | 576篇 |
2000年 | 457篇 |
1999年 | 552篇 |
1998年 | 636篇 |
1997年 | 486篇 |
1996年 | 425篇 |
1995年 | 411篇 |
1994年 | 374篇 |
1993年 | 361篇 |
1992年 | 411篇 |
1991年 | 347篇 |
1990年 | 291篇 |
1989年 | 289篇 |
1988年 | 296篇 |
1987年 | 277篇 |
1986年 | 252篇 |
1985年 | 320篇 |
1984年 | 342篇 |
1983年 | 279篇 |
1982年 | 368篇 |
1981年 | 295篇 |
1980年 | 265篇 |
1979年 | 206篇 |
1978年 | 234篇 |
1977年 | 219篇 |
1976年 | 182篇 |
1975年 | 177篇 |
1974年 | 202篇 |
1973年 | 211篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Pierre Valeix Paul Preziosi Claude Rossignol Marie-Alice Farnier Serge Hercberg 《Biological trace element research》1992,32(1-3):259-266
Urinary iodine excretion was assessed in 642 healthy children aged 10 mo (n=243), 2 yr (n=183), and 4 yr (n=216) living in the Paris area and originating from continental France (60.3%), North Africa (13.8%), the West Indies (9.1%),
West Africa (8.3%), Southeast Asia (4.8%), and southern Europe (3.8%). Mild impairment of neurological (reflexes, tone, audiometry)
and intellectual development (Brunet-Lézine scale) was assessed in relation to iodine status. Iodine excretions (median values)
were 18.4, 11.9, and 10.9 μg/100 mL at 10 mo, 2 yr, and 4 yr, respectively, and risk of mild iodine deficiency (5–10 μg/100
mL) was 18.1%, 34.8%, and 38.3% for the same age groups. No relationship was found between anthropometry, global development
quotient, and iodine status. High hearing thresholds were more commonly associated with lower iodine excretion, suggesting
mild hearing defects. In spite of iodine prophylaxis, the risk of mild to moderate iodine deficiency still exists in France
and in a number of European countries. Evaluation of neurological sequels of borderline iodine status is a major public health
problem in European communities. 相似文献
992.
Momčilo Mihailović Paul Lindberg Ivan Jovanović Duŝan Antić 《Biological trace element research》1992,33(1-3):71-77
The selenium (Se) contents in common cereals in endemic and nonendemic areas in Serbia are very low. Plasma Se levels of both
patients and healthy subjects, were also low, reflecting low Se intakes. Patients with Balkan endemic nephropathy (BEN) had
significantly lower (p<0.05) plasma Se levels than healthy individuals, both from regions close to endemic areas, and from Belgrade. Mean plasma
Se of BEN patients was slightly but insignificantly higher in samples taken immediately after dialysis than in those taken
before, suggesting that very little of the Se present in plasma is dialyzable. Plasma SeGSH-Px activities before and after
hemodialysis in both BEN and Nonendemic chronic renal failure (NCRF) patients were not significantly different, but BEN patients
had lower enzyme activities than those with NCRF and healthy controls. In BEN patients, a significant correlation between
plasma Se and SeGSH-Px activity was found.
NCFR patients were with diagnoses: TBC of kidneys, chronic glomerulonephritis, chronic pyelonephritis, and polycystic kidneys. 相似文献
993.
Three new species of coccidian were recovered from the intestinal contents and faeces of lizards in Namibia, southwest Africa. Oöcysts of Eimeria barnardi n. sp. are described from Rhoptropus barnardi (Gekkonidae) and are ellipsoidal, 24.3 × 19.9 (21–26.5 × 16–22) m; shape index (length/width) 1.22 (1.12–1.30). A micropyle and oöcyst residuum are absent but a fragmented polar granule is present. Sporocysts are subspherical, 9.2 × 8.3 (8–11 × 7.5–9) m; shape index 1.11 (1.02–1.27). Oöcysts of Eimeria pachybibroni n. sp. were found in Pachydactylus bibroni (Gekkonidae) and are ellipsoidal, 26.2 × 18.2 (21.5–28 × 16–19) m; shape index 1.44 (1.30–1.52). A micropyle and oöcyst residuum are absent but a polar granule is present. Sporocysts are subspherical, 8.9 × 8.0 (8–9.5 × 7–8.5) m; shape index 1.12 (1.03–1.20). Oöcysts of Isospora spilogaster n. sp. are reported from Mabuya spilogaster (Scincidae) and are subspherical, 27.4 × 26.0 (21.5–35 × 21–35) m; shape index 1.05 (1.00–1.13). Micropyle, oöcyst residuum and polar granules are absent. Sporocysts are ellipsoidal, 13.2 × 9.7 (10.5–15 × 9–11) m; shape index 1.36 (1.08–1.50). 相似文献
994.
Pilar Galan Helene Thibault Paul Preziosi Serge Hercberg 《Biological trace element research》1992,32(1-3):421-426
The relationship between iron status and capacity for IL-2 production by lymphocytes was assessed in 81 children from 6 mo
to 3 yr of age selected at random from a population with low socioeconomic status, undergoing free systematic examination
in four children's health centers in the Paris area. Iron deficiency was defined by the existence of at least two abnormal
values among the three indicators of iron status: serum ferritin level ≤12 μg/L, transferrin saturation <12%, and erythrocyte
protoporphyrin concentration >3 μg/g hemoglobin. According to this definition, 53 children were classified as iron deficient
and 28 as iron sufficient. No differences were observed between the iron-deficient and iron-sufficient groups in terms of
the IL-2 concentration without stimulation by PHA. IL-2 production by lymphocytes stimulated with PHA, as well as the stimulation
index (ratio of IL-2 concentration following stimulation by PHA to that of IL-2 concentration without stimulation by PHA)
were significantly lower in iron-deficient children. The reduction in IL-2 production by activated lymphocytes observed in
our study of iron-deficient children may be responsible for impairments in immunity found by other authors, particularly in
cell-mediated immunity. 相似文献
995.
996.
997.
998.
Agrobacterium and plant genetic engineering 总被引:27,自引:0,他引:27
Erratum
Agrobacterium and plant genetic engineering 相似文献999.
Summary Cellobiose oxidase from Phanerochaete chrysosporium was used for continuous monitoring of cellulase action on microcrystalline cellulose (Avicel). Two protocols are described, the parameter monitored being either the decline in electrode potential as ferricyanide is reduced or consumption of dioxygen. Most experiments used a commercial cellulase preparation from Trichoderma reesei and ferricyanide as acceptor. Within 1 min of an addition of cellulase, ferricyanide reduction reached a steady rate. This was converted into a rate of production of substrate for celobiose oxidase, in mol·min–1. Experiments were conducted either with a constant concentration of cellulase and increasing Avicel, or with constant Avicel and increasing cellulase. Kinetic analysis of the experiments with constant cellulase indicated a K
mof 4.8 ± 1.0 (g cellulose)·1–1, which was close to the value predicted from binding studies. The specific activity of the cellulase was measured as 375±25 mol·(g cellulase)–1·min–1 in experiments with a high cellulose concentration, but was less than half this value when the cellulose was saturated with cellulase. The maximal rate of cellulose degradation was 9.6±1.3 mol·(g cellulose)–1·min–1. 相似文献
1000.