全文获取类型
收费全文 | 2460篇 |
免费 | 224篇 |
国内免费 | 1篇 |
出版年
2023年 | 17篇 |
2022年 | 31篇 |
2021年 | 49篇 |
2020年 | 41篇 |
2019年 | 58篇 |
2018年 | 81篇 |
2017年 | 61篇 |
2016年 | 99篇 |
2015年 | 131篇 |
2014年 | 145篇 |
2013年 | 160篇 |
2012年 | 225篇 |
2011年 | 198篇 |
2010年 | 144篇 |
2009年 | 112篇 |
2008年 | 133篇 |
2007年 | 111篇 |
2006年 | 113篇 |
2005年 | 80篇 |
2004年 | 94篇 |
2003年 | 93篇 |
2002年 | 81篇 |
2001年 | 35篇 |
2000年 | 35篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 19篇 |
1996年 | 19篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 17篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1966年 | 6篇 |
排序方式: 共有2685条查询结果,搜索用时 31 毫秒
81.
Specimens of the hard tick Amblyomma triste were found infected with Rickettsia parkeri in an area of Argentina (General Lavalle, Buenos Aires Province) where cases of human illness attributed to this microorganism have been reported. Molecular detection of R. parkeri was based on polymerase chain reactions that amplify a ca. 400-bp fragment of the 23S-5S intergenic spacer and a ca. 500-bp fragment of the gene encoding a 190-kDa outer membrane protein. Three (6.97%) of 43 A. triste ticks were determined to be positive for R. parkeri. These results provide strong evidence that A. triste is the vector of R. parkeri in the study area. The findings of this work have epidemiological relevance because human parasitism by A. triste ticks has been frequently recorded in some riparian areas of Argentina and Uruguay and new cases of R. parkeri rickettsiosis might arise in the South American localities where humans are exposed to the bites of this tick species. 相似文献
82.
Francisco Meijide Juan V. Trillo Santiago de Frutos Luciano Galantini Nicolae Viorel Pavel Victor H. Soto Aida Jover José Vázquez Tato 《Steroids》2013,78(2):247-254
The crystal structure of three head-to-head dimers (having two cholic acid or deoxycholic acid units) linked at carbon atoms C3 by aromatic or alkyl bridges is studied. An internal coordinates system is necessary for describing the relative orientation in the space of the two bile acid residues. Five angles (three torsion and two common ones) are necessary for defining the relative position of both steroid residues in space. Carbon atoms C3 (which always carries a α-hydroxy group in natural bile acids), and C10 and C13 (which always carry β-methyl groups) of each steroid residue are suitable for this purpose. Furthermore, the distance between each C3 carbon atoms of both steroid residues will allow one to locate the steroids in space. The three dimers selected provide a large range of values for these angles. The packing, hydrogen bond network, and location of guest in the three crystals are discussed. 相似文献
83.
Julio O. Giordano Milo C. Wiltbank Paul M. Fricke Santiago Bas Ray Pawlisch Jerry N. Guenther Anibal B. Nascimento 《Theriogenology》2013
Ovsynch-type synchronization of ovulation protocols have suboptimal synchronization rates due to reduced ovulation to the first GnRH treatment and inadequate luteolysis to the prostaglandin F2α (PGF2α) treatment before timed artificial insemination (TAI). Our objective was to determine whether increasing the dose of the first GnRH or the PGF2α treatment during the Breeding-Ovsynch portion of Double-Ovsynch could improve the rates of ovulation and luteolysis and therefore increase pregnancies per artificial insemination (P/AI). In experiment 1, cows were randomly assigned to a two-by-two factorial design to receive either a low (L) or high (H) doses of GnRH (Gonadorelin; 100 vs. 200 μg) and a PGF2α analogue (cloprostenol; 500 vs. 750 μg) resulting in the following treatments: LL (n = 263), HL (n = 277), LH (n = 270), and HH (n = 274). Transrectal ultrasonography and serum progesterone (P4) were used to assess ovulation to GnRH1, GnRH2, and luteal regression after PGF2α during Breeding-Ovsynch in a subgroup of cows (n = 651 at each evaluation). Pregnancy status was assessed 29, 39, and 74 days after TAI. In experiment 2, cows were randomly assigned to LL (n = 220) or HH (n = 226) treatment as described for experiment 1. For experiment 1, ovulation to GnRH1 was greater (P = 0.01) for cows receiving H versus L GnRH (66.6% [217/326] vs. 57.5% [187/325]) treatment, but only for cows with elevated P4 at GnRH1. Cows that ovulated to GnRH1 had increased (P < 0.001) fertility compared with cows that did not ovulate (52.2% vs. 38.5%); however, no effect of higher dose of GnRH on fertility was detected. The greater PGF2α dose increased luteal regression primarily in multiparous cows (P = 0.03) and tended to increase fertility (P = 0.05) only at the pregnancy diagnosis 39 days after TAI. Overall, P/AI was 47.0% at 29 days and 39.7% at 74 days after TAI; P/AI did not differ (P = 0.10) among treatments at 74 days (LL, 34.6%; HL, 40.8%; LH, 42.2%; HH, 40.9%) and was greater (P < 0.001) for primiparous cows than for multiparous cows (46.1% vs. 33.8%). For experiment 2, P/AI did not differ (P = 0.21) between H versus L treatments (44.2% [100/226] vs. 40.5% [89/220]). Thus, despite an increase in ovulatory response to GnRH1 and luteal regression to PGF2α, there were only marginal effects of increasing dose of GnRH or PGF2α on fertility to TAI after Double-Ovsynch. 相似文献
84.
85.
Josué Martínez‐de la Puente Santiago Merino Elisa Lobato Juan Moreno Gustavo Tomás Judith Morales 《Bird Study》2013,60(2):264-267
Capsule Some males brought building materials to nests and females who were paired with such males laid heavier clutches. 相似文献
86.
87.
Cynthia Maria De Lyra Neves Carlos Alfredo Lopes De Carvalho Cerilene Santiago Machado Fernanda Silva Das Mercês Sousa 《Grana》2013,52(4):302-308
Pollen analysis of the larval food supply is an important tool for identifying the plants that provide the floral resources used by bees. The present study documents the pollen sources consumed by larvae of the solitary bee Tetrapedia diversipes in a tropical agroecosystem. A total of 60 pollen types were recorded with three families being the most important. Euphorbiaceae (60.5%), Malpighiaceae (16.8%) and Asteraceae (12.2%) pollen had the greatest representation in the samples examined. The pollen of Dalechampia dioscoreifolia predominated in the diet of the larvae of T. diversipes (RF?=?56.35%) and indicates the importance of this plant in maintaining populations of this solitary bee. 相似文献
88.
Stephen Mosher Heike Seybold Patricia Rodriguez Mark Stahl Kelli A. Davies Sajeewani Dayaratne Santiago A. Morillo Michael Wierzba Bruno Favery Harald Keller Frans E. Tax Birgit Kemmerling 《The Plant journal : for cell and molecular biology》2013,73(3):469-482
The tyrosine‐sulfated peptides PSKα and PSY1 bind to specific leucine‐rich repeat surface receptor kinases and control cell proliferation in plants. In a reverse genetic screen, we identified the phytosulfokine (PSK) receptor PSKR1 as an important component of plant defense. Multiple independent loss‐of‐function mutants in PSKR1 are more resistant to biotrophic bacteria, show enhanced pathogen‐associated molecular pattern responses and less lesion formation after infection with the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. By contrast, pskr1 mutants are more susceptible to necrotrophic fungal infection with Alternaria brassicicola, show more lesion formation and fungal growth which is not observed on wild‐type plants. The antagonistic effect on biotrophic and necrotrophic pathogen resistance is reflected by enhanced salicylate and reduced jasmonate responses in the mutants, suggesting that PSKR1 suppresses salicylate‐dependent defense responses. Detailed analysis of single and multiple mutations in the three paralogous genes PSKR1, ‐2 and PSY1‐receptor (PSY1R) determined that PSKR1 and PSY1R, but not PSKR2, have a partially redundant effect on plant immunity. In animals and plants, peptide sulfation is catalyzed by a tyrosylprotein sulfotransferase (TPST). Mutants lacking TPST show increased resistance to bacterial infection and increased susceptibility to fungal infection, mimicking the triple receptor mutant phenotypes. Feeding experiments with PSKα in tpst‐1 mutants partially restore the defense‐related phenotypes, indicating that perception of the PSKα peptide has a direct effect on plant defense. These results suggest that the PSKR subfamily integrates growth‐promoting and defense signals mediated by sulfated peptides and modulates cellular plasticity to allow flexible adjustment to environmental changes. 相似文献
89.
V. H. P. Bueno J. C. van Lenteren J. C. Lins Jr A. M. Calixto F. C. Montes D. B. Silva L. D. Santiago L. M. Pérez 《Journal of Applied Entomology》2013,137(1-2):29-34
The tomato borer Tuta absoluta, native to western South America, is an extremely devastating pest in tomato crops in most of South America, Europe and Africa North of the Sahel, causes yield losses up to 100% and decreases fruit quality in open field and greenhouse crops if control methods are not applied. In Brazil two other important lepidopteran pests – Neoleucinodes elegantalis and Helicoverpa zea – occur in tomato, as well as thrips, whiteflies and aphids. For control of these pests, frequent applications of pesticides of up to 5 times per week are needed, and these resulted in the appearance of resistant populations to a number of active ingredients and decimation of natural enemies. Biological control may offer a better, safer and more sustainable opportunity for pest management. Mirid predatory bugs are currently used with success in southern Europe to control T. absoluta and other pests. In Brazil, four Hemipteran predatory bugs, not yet known to attack T. absoluta, were found to successfully prey on eggs and larvae of this pest. The first results on their predation capacity, development, survival and reproduction on T. absoluta on tomato plants are presented. 相似文献
90.
Diego Santiago‐Alarcon Raeann Mettler Gernot Segelbacher H. Martin Schaefer 《Journal of avian biology》2013,44(6):521-530
Parasites can exert strong selection on hosts. Throughout the year migrants are exposed to different sets of parasites, which may affect life history traits such as migratory schedules. Here, we studied the relationship between parasite infection and arrival date of blackcaps Sylvia atricapilla to their breeding grounds in Germany throughout a period of six years (2007–2012). We used two data sets, one that included all blackcaps and one that included only recaptured birds. We assesed whether parasites influence spring arrival to breeding grounds, and for the recaptured data set, we analysed temporal variation in parasitism (i.e. infection status and parasitaemia) throughout the breeding season. We used both microscopy and PCR (a fragment of ? 479 bp of the mtDNA cyt b) to determine haemosporidian infection. Blackcaps were mostly infected with Haemoproteus parabelopolskyi (lineages SYAT01 and SYAT02). Infection status, but not parasitaemia, was constant through time for individual birds; meaning that once a bird is infected, it most likely will retain the infection for life. We found that infection by haemosporidian parasites has no relationship to arrival date in this blackcap population; however, infection by H. parabelopolskyi has a marginally significant effect on arrival date of recaptured blackcaps, somewhat delaying their arrival to breeding grounds. Birds captured later in the season were more likely to be infected than those from early spring, and parasitaemia was frequently lower in birds captured earlier in the season compared to those captured later (summer). 相似文献